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The Different Forms of Flowers on Plants of the Same Species
by Charles Darwin
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In close connection with the lesser potency of the two kinds of pollen of the mid-styled form is the fact that, according to H. Muller, the grains of both are a little less in diameter than the corresponding grains produced by the other two forms. Thus the grains from the longest stamens of the mid-styled form are 9 to 10, whilst those from the corresponding stamens of the short-styled form are 9 1/2 to 10 1/2 in diameter. So, again, the grains from the shortest stamens of the mid-styled are 6, whilst those from the corresponding stamens of the long- styled are 6 to 6 1/2 in diameter. It would thus appear as if the male organs of the mid-styled form, though not as yet rudimentary, were tending in this direction. On the other hand, the female organs of this form are in an eminently efficient state, for the naturally fertilised capsules yielded a considerably larger average number of seeds than those of the other two forms—almost every flower which was artificially fertilised in a legitimate manner produced a capsule—and most of the illegitimate unions were highly productive. The mid- styled form thus appears to be highly feminine in nature; and although, as just remarked, it is impossible to consider its two well-developed sets of stamens which produce an abundance of pollen as being in a rudimentary condition, yet we can hardly avoid connecting as balanced the higher efficiency of the female organs in this form with the lesser efficiency and lesser size of its two kinds of pollen-grains. The whole case appears to me a very curious one.

It may be observed in Tables 4.23 to 4.25 that some of the illegitimate unions yielded during neither year a single seed; but, judging from the long-styled plants, it is probable, if such unions were to be effected repeatedly by the aid of insects under the most favourable conditions, some few seeds would be produced in every case. Anyhow, it is certain that in all twelve illegitimate unions the pollen-tubes penetrated the stigma in the course of eighteen hours. At first I thought that two kinds of pollen placed together on the same stigma would perhaps yield more seed than one kind by itself; but we have seen that this is not so with each form's own two kinds of pollen; nor is it probable in any case, as I occasionally got, by the use of a single kind of pollen, fully as many seeds as a capsule naturally fertilised ever produces. Moreover the pollen from a single anther is far more than sufficient to fertilise fully a stigma; hence, in this as with so many other plants, more than twelve times as much of each kind of pollen is produced as is necessary to ensure the full fertilisation of each form. From the dusted condition of the bodies of the bees which I caught on the flowers, it is probable that pollen of various kinds is often deposited on all three stigmas; but from the facts already given with respect to the two forms of Primula, there can hardly be a doubt that pollen from the stamens of corresponding length placed on a stigma would be prepotent over any other kind of pollen and obliterate its effects,—even if the latter had been placed on the stigma some hours previously.

Finally, it has now been shown that Lythrum salicaria presents the extraordinary case of the same species bearing three females, different in structure and function, and three or even five sets (if minor differences are considered) of males; each set consisting of half-a-dozen, which likewise differ from one another in structure and function.

[Lythrum Graefferi.

I have examined numerous dried flowers of this species, each from a separate plant, sent me from Kew. Like L. salicaria, it is trimorphic, and the three forms apparently occur in about equal numbers. In the long-styled form the pistil projects about one-third of the length of the calyx beyond its mouth, and is therefore relatively much shorter than in L. salicaria; the globose and hirsute stigma is larger than that of the other two forms; the six mid-length stamens, which are graduated in length, have their anthers standing close above and close beneath the mouth of the calyx; the six shortest stamens rise rather above the middle of the calyx. In the mid-styled form the stigma projects just above the mouth of the calyx, and stands almost on a level with the mid-length stamens of the long and short-styled forms; its own longest stamens project well above the mouth of the calyx, and stand a little above the level of the stigma of the long-styled form. In short, without entering on further details, there is a close general correspondence in structure between this species and L. salicaria, but with some differences in the proportional lengths of the parts. The fact of each of the three pistils having two sets of stamens of corresponding lengths, borne by the two other forms, comes out conspicuously. In the mid-styled form the pollen-grains from the longest stamens are nearly double the diameter of those from the shortest stamens; so that there is a greater difference in this respect than in L. salicaria. In the long-styled form, also, the difference in diameter between the pollen-grains of the mid-length and shortest stamens is greater than in L. salicaria. These comparisons, however, must be received with caution, as they were made on specimens soaked in water after having been long kept dry.

Lythrum thymifolia.

This form, according to Vaucher, is dimorphic, like Primula, and therefore presents only two forms. (4/8. 'Hist. Phys. des Plantes d'Europe' tome 2 1841 pages 369, 371.) I received two dried flowers from Kew, which consisted of the two forms; in one the stigma projected far beyond the calyx, in the other it was included within the calyx; in this latter form the style was only one-fourth of the length of that in the other form. There are only six stamens; these are somewhat graduated in length, and their anthers in the short-styled form stand a little above the stigma, but yet by no means equal in length the pistil of the long-styled form. In the latter the stamens are rather shorter than those in the other form. The six stamens alternate with the petals, and therefore correspond homologically with the longest stamens of L. salicaria and L. Graefferi.

Lythrum hyssopifolia.

This species is said by Vaucher, but I believe erroneously, to be dimorphic. I have examined dried flowers from twenty-two separate plants from various localities, sent to me by Mr. Hewett C. Watson, Professor Babington, and others. These were all essentially alike, so that the species cannot be heterostyled. The pistil varies somewhat in length, but when unusually long, the stamens are likewise generally long; in the bud the stamens are short; and Vaucher was perhaps thus deceived. There are from six to nine stamens, graduated in length. The three stamens, which vary in being either present or absent, correspond with the six shorter stamens of L. salicaria and with the six which are always absent in L. thymifolia. The stigma is included within the calyx, and stands in the midst of the anthers, and would generally be fertilised by them; but as the stigma and anthers are upturned, and as, according to Vaucher, there is a passage left in the upper side of the flower to the nectary, there can hardly be a doubt that the flowers are visited by insects, and would occasionally be cross-fertilised by them, as surely as the flowers of the short-styled L. salicaria, the pistil of which and the corresponding stamens in the other two forms closely resemble those of L. hyssopifolia. According to Vaucher and Lecoq, this species, which is an annual, generally grows almost solitarily (4/9. 'Geograph. Bot. de l'Europe' tome 6 1857 page 157.), whereas the three preceding species are social; and this fact alone would almost have convinced me that L. hyssopifolia was not heterostyled, as such plants cannot habitually live isolated any better than one sex of a dioecious species.

We thus see that within this genus some species are heterostyled and trimorphic; one apparently heterostyled and dimorphic, and one homostyled.

Nesaea verticillata.

I raised a number of plants from seed sent me by Professor Asa Gray, and they presented three forms. These differed from one another in the proportional lengths of their organs of fructification and in all respects, in very nearly the same way as the three forms of Lythrum Graefferi. The green pollen-grains from the longest stamens, measured along their longer axis and not distended with water, were 13/7000 of an inch in length; those from the mid-length stamens 9 to 10/7000, and those from the shortest stamens 8 to 9/7000 of an inch. So that the largest pollen-grains are to the smallest in diameter as 100 to 65. This plant inhabits swampy ground in the United States. According to Fritz Muller, a species of this genus in St. Catharina, in Southern Brazil, is homostyled. (4/10. 'Botanische Zeitung' 1868 page 112.)

Lagerstroemia Indica.

This plant, a member of the Lythraceae, may perhaps be heterostyled, or may formerly have been so. It is remarkable from the extreme variability of its stamens. On a plant, growing in my hothouse, the flowers included from nineteen to twenty-nine short stamens with yellow pollen, which correspond in position with the shortest stamens of Lythrum; and from one to five (the latter number being the commonest) very long stamens, with thick flesh-coloured filaments and green pollen, corresponding in position with the longest stamens of Lythrum. In one flower, two of the long stamens produced green, while a third produced yellow pollen, although the filaments of all three were thick and flesh- coloured. In an anther of another flower, one cell contained green and the other yellow pollen. The green and yellow pollen-grains from the stamens of different length are of the same size. The pistil is a little bowed upwards, with the stigma seated between the anthers of the short and long stamens, so that this plant was mid-styled. Eight flowers were fertilised with green pollen, and six with yellow pollen, but not one set fruit. This latter fact by no means proves that the plant is heterostyled, as it may belong to the class of self-sterile species. Another plant growing in the Botanic Gardens at Calcutta, as Mr. J. Scott informs me, was long-styled, and it was equally sterile with its own pollen; whilst a long-styled plant of L. reginae, though growing by itself, produced fruit. I examined dried flowers from two plants of L. parviflora, both of which were long-styled, and they differed from L. Indica in having eight long stamens with thick filaments, and a crowd of shorter stamens. Thus the evidence whether L. Indica is heterostyled is curiously conflicting: the unequal number of the short and long stamens, their extreme variability, and especially the fact of their pollen-grains not differing in size, are strongly opposed to this belief; on the other hand, the difference in length of the pistils in two of the plants, their sterility with their own pollen, and the difference in length and structure of the two sets of stamens in the same flower, and in the colour of their pollen, favour the belief. We know that when plants of any kind revert to a former condition, they are apt to be highly variable, and the two halves of the same organ sometimes differ much, as in the case of the above-described anther of the Lagerstroemia; we may therefore suspect that this species was once heterostyled, and that it still retains traces of its former state, together with a tendency to revert more completely to it. It deserves notice, as bearing on the nature of Lagerstroemia, that in Lythrum hyssopifolia, which is a homostyled species, some of the shorter stamens vary in being either present or absent; and that these same stamens are altogether absent in L. thymifolia. In another genus of the Lythraceae, namely Cuphea, three species raised by me from seed certainly were homostyled; nevertheless their stamens consisted of two sets, differing in length and in the colour and thickness of their filaments, but not in the size or colour of their pollen-grains; so that they thus far resembled the stamens of Lagerstroemia. I found that Cuphea purpurea was highly fertile with its own pollen when artificially aided, but sterile when insects were excluded. (4/11. Mr. Spence informs me that in several species of the genus Mollia (Tiliaceae) which he collected in South America, the stamens of the five outer cohorts have purplish filaments and green pollen, whilst the stamens of the five inner cohorts have yellow pollen. He therefore suspected that these species might prove to be heterostyled and trimorphic: but he did not notice the length of the pistils. In the allied Luhea the outer purplish stamens are destitute of anthers. I procured some specimens of Mollia lepidota and speciosa from Kew, but could not make out that their pistils differed in length in different plants; and in all those which I examined the stigma stood close beneath the uppermost anthers. The numerous stamens are graduated in length, and the pollen-grains from the longest and shortest ones did not present any marked difference in diameter. Therefore these species do not appear to be heterostyled.)]

Oxalis (Geraniaceae).

(Figure 4.11. Oxalis speciosa (with the petals removed). Left: Long-styled. Centre: Mid-styled. Right: Short-styled. S, S, S, stigmas. The dotted lines with arrows show which pollen must be carried to the stigmas for legitimate fertilisation.)

In 1863 Mr. Roland Trimen wrote to me from the Cape of Good Hope that he had there found species of Oxalis which presented three forms; and of these he enclosed drawings and dried specimens. Of one species he collected 43 flowers from distinct plants, and they consisted of 10 long-styled, 12 mid-styled, and 21 short-styled. Of another species he collected 13 flowers, consisting of 3 long-styled, 7 mid-styled, and 3 short-styled. In 1866 Professor Hildebrand proved by an examination of the specimens in several herbaria that 20 species are certainly heterostyled and trimorphic, and 51 others almost certainly so. (4/12. 'Monatsber. der Akad. der Wiss. Berlin' 1866 pages 352, 372. He gives drawings of the three forms at page 42 of his 'Geschlechter-Vertheilung' etc. 1867.) He also made some interesting observations on living plants belonging to one form alone; for at that time he did not possess the three forms of any living species. During the years 1864 to 1868 I occasionally experimented on Oxalis speciosa, but until now have never found time to publish the results. In 1871 Hildebrand published an admirable paper in which he shows in the case of two species of Oxalis, that the sexual relations of the three forms are nearly the same as in Lythrum salicaria. (4/13. 'Botanische Zeitung' 1871 pages 416 and 432.) I will now give an abstract of his observations, and afterwards of my own less complete ones. I may premise that in all the species seen by me, the stigmas of the five straight pistils of the long-styled form stand on a level with the anthers of the longest stamens in the two other forms. In the mid- styled form, the stigmas pass out between the filaments of the longest stamens (as in the short-styled form of Linum); and they stand rather nearer to the upper anthers than to the lower ones. In the short-styled form, the stigmas also pass out between the filaments nearly on a level with the tips of the sepals. The anthers in this latter form and in the mid-styled rise to the same height as the corresponding stigmas in the other two forms.

Oxalis Valdiviana.

This species, an inhabitant of the west coast of South America, bears yellow flowers. Hildebrand states that the stigmas of the three forms do not differ in any marked manner, but that the pistil of the short-styled form alone is destitute of hairs. The diameters of the pollen-grains are as follows:—

Table 4.b. Oxalis Valdiviana. Diameters of pollen-grains in divisions of the micrometer.

Column 1: Source of Pollen-grains. Column 2: Minimum diameter. Column 3: Maximum diameter.

From the: Longest stamens of short-styled form : 8 to 9. Mid-length stamens of short-styled form : 7 to 8. Longest stamens of mid-styled form : 8. Shortest stamens of mid-styled form : 8. Mid-length stamens of long-styled form : 7. Shortest stamens of long-styled form : 6.

Therefore the extreme difference in diameter is as 8.5 to 6, or as 100 to 71. The results of Hildebrand's experiments are given in Table 4.27, drawn up in accordance with my usual plan.

Table 4.27. Oxalis Valdiviana (from Hildebrand).

Column 1: Nature of the Union. Column 2: Number of Flowers fertilised. Column 3: Number of Capsules produced. Column 4: Number of Seeds per Capsule.

Long-styled by pollen of longest stamens of short-styled. Legitimate union : 28 : 28 : 11.9.

Long-styled by pollen of longest stamens of mid-styled. Legitimate union : 21 : 21 : 12.0.

Long-styled by pollen of own and own-form mid-length stamens. Illegitimate union : 40 : 2 : 5.5.

Long-styled by pollen of own and own-form shortest stamens. Illegitimate union : 26 : 0 : 0.

Long-styled by pollen of shortest stamens of short-styled. Illegitimate union : 16 : 1 : 1.

Long-styled by pollen of shortest stamens of mid-styled. Illegitimate union : 9 : 0 : 0.

Mid-styled by pollen of mid-length stamens of long-styled. Legitimate union : 38 : 38 : 11.3.

Mid-styled by pollen of mid-length stamens of short-styled. Legitimate union : 23 : 23 : 10.4.

Mid-styled by pollen of own and own-form longest stamens. Illegitimate union : 52 : 0 : 0.

Mid-styled by pollen of own and own-form shortest stamens. Illegitimate union : 30 : 1 : 6.

Mid-styled by pollen of shortest stamens of long-styled. Illegitimate union : 16 : 0 : 0.

Mid-styled by pollen of longest stamens of short-styled. Illegitimate union : 16 : 2 : 2.5.

Short-styled by pollen of shortest stamens of long-styled. Legitimate union: 18 : 18 : 11.0.

Short-styled by pollen of shortest stamens of mid-styled. Legitimate union: 10 : 10 : 11.3.

Short-styled by pollen of own and own-form longest stamens. Illegitimate union : 21 : 0 : 0.

Short-styled by pollen of own and own-form mid-length stamens. Illegitimate union : 22 : 0 : 0.

Short-styled by pollen of longest stamens of mid-styled. Illegitimate union: 4 : 0 : 0.

Short-styled by pollen of mid-length stamens of long-styled. Illegitimate union: 3 : 0 : 0.

We here have the remarkable result that every one of 138 legitimately fertilised flowers on the three forms yielded capsules, containing on an average 11.33 seeds. Whilst of the 255 illegitimately fertilised flowers, only 6 yielded capsules, which contained 3.83 seeds on an average. Therefore the fertility of the six legitimate to that of the twelve illegitimate unions, as judged by the proportion of flowers that yielded capsules, is as 100 to 2, and as judged by the average number of seeds per capsule as 100 to 34. It may be added that some plants which were protected by nets did not spontaneously produce any fruit; nor did one which was left uncovered by itself and was visited by bees. On the other hand, scarcely a single flower on some uncovered plants of the three forms growing near together failed to produce fruit.

Oxalis Regnelli.

This species bears white flowers and inhabits Southern Brazil. Hildebrand says that the stigma of the long-styled form is somewhat larger than that of the mid- styled, and this than that of the short-styled. The pistil of the latter is clothed with a few hairs, whilst it is very hairy in the other two forms. The diameter of the pollen-grains from both sets of the longest stamens equals 9 divisions of the micrometer,—that from the mid-length stamens of the long- styled form between 8 and 9, and of the short-styled 8,—and that from the shortest stamens of both sets 7. So that the extreme difference in diameter is as 9 to 7 or as 100 to 78. The experiments made by Hildebrand, which are not so numerous as in the last case, are given in Table 4.28 in the same manner as before.

TABLE 4.28. Oxalis Regnelli (from Hildebrand).

Column 1: Nature of the Union. Column 2: Number of Flowers fertilised. Column 3: Number of Capsules produced. Column 4: Average Number of Seeds per Capsule.

Long-styled by pollen of longest stamens of short-styled. Legitimate union : 6 : 6 : 10.1.

Long-styled by pollen of longest stamens of mid-styled. Legitimate union : 5 : 5 : 10.6.

Long-styled by pollen of own mid-length stamens. Illegitimate union : 4 : 0 : 0.

Long-styled by pollen of own shortest stamens. Illegitimate union : 1 : 0 : 0.

Mid-styled by pollen of mid-length stamens of short-styled. Legitimate union : 9 : 9 : 10.4.

Mid-styled by pollen of mid-length stamens of long-styled. Legitimate union : 10 : 10 : 10.1.

Mid-styled by pollen of own longest stamens. Illegitimate union : 9 : 0 : 0.

Mid-styled by pollen of own shortest stamens. Illegitimate union : 2 : 0 : 0.

Mid-styled by pollen of longest stamens of short-styled. Illegitimate union : 1 : 0 : 0.

Short-styled by pollen of shortest stamens of mid-styled. Legitimate union: 9 : 9 : 10.6.

Short-styled by pollen of shortest stamens of long-styled. Legitimate union: 2 : 2 : 9.5.

Short-styled by pollen of own mid-length stamens. Illegitimate union : 12 : 0 : 0.

Short-styled by pollen of own longest stamens. Illegitimate union : 9 : 0 : 0.

Short-styled by pollen of mid-length stamens of long-styled. Illegitimate union: 1 : 0 : 0.

The results are nearly the same as in the last case, but more striking; for 41 flowers belonging to the three forms fertilised legitimately all yielded capsules, containing on an average 10.31 seeds; whilst 39 flowers fertilised illegitimately did not yield a single capsule or seed. Therefore the fertility of the six legitimate to that of the several illegitimate unions, as judged both by the proportion of flowers which yielded capsules and by the average number of contained seeds, is as 100 to 0.

Oxalis speciosa.

This species, which bears pink flowers, was introduced from the Cape of Good Hope. A sketch of the reproductive organs of the three forms (Figure 4.11) has already been given. The stigma of the long-styled form (with the papillae on its surface included) is twice as large as that of the short-styled, and that of the mid-styled intermediate in size. The pollen-grains from the stamens in the three forms are in their longer diameters as follows:—

Table 4.c. Oxalis speciosa. Diameters of pollen-grains in divisions of the micrometer.

Column 1: Source of Pollen-grains. Column 2: Minimum diameter. Column 3: Maximum diameter.

From the: Longest stamens of short-styled form : 15 to 16. Mid-length stamens of short-styled form : 12 to 13. Longest stamens of mid-styled form : 16. Shortest stamens of mid-styled form : 11 to 12. Mid-length stamens of long-styled form : 14. Shortest stamens of long-styled form : 12.

Therefore the extreme difference in diameter is as 16 to 11, or as 100 to 69; but as the measurements were taken at different times, they are probably only approximately accurate. The results of my experiments in fertilising the three forms are given in Table 4.29.

Table 4.29. Oxalis speciosa.

Column 1: Nature of the Union. Column 2: Number of Flowers fertilised. Column 3: Number of Capsules produced. Column 4: Average Number of Seeds per Capsule.

Long-styled by pollen of longest stamens of short-styled. Legitimate union : 19 : 15 : 57.4.

Long-styled by pollen of longest stamens of mid-styled. Legitimate union : 4 : 3 : 59.0.

Long-styled by pollen of own-form mid-length stamens. Illegitimate union : 9 : 2 : 42.5.

Long-styled by pollen of own-form shortest stamens. Illegitimate union : 11 : 0 : 0.

Long-styled by pollen of shortest stamens of mid-styled. Illegitimate union : 4 : 0 : 0.

Long-styled by pollen of mid-length stamens of short-styled. Illegitimate union : 12 : 5 : 30.0.

Mid-styled by pollen of mid-length stamens of long-styled. Legitimate union : 3 : 3 : 63.6.

Mid-styled by pollen of mid-length stamens of short-styled. Legitimate union : 4 : 4 : 56.3.

Mid-styled by mixed pollen from both own-form longest and shortest stamens. Illegitimate union : 9 : 2 : 19.

Mid-styled by pollen of longest stamens of short-styled. Illegitimate union : 12 : 1 : 8.

Short-styled by pollen of shortest stamens of mid-styled. Legitimate union: 3 : 2 : 67.

Short-styled by pollen of shortest stamens of long-styled. Legitimate union: 3 : 3 : 54.3.

Short-styled by pollen of own-form longest stamens. Illegitimate union: 5 : 1 : 8.

Short-styled by pollen of own-form mid-length stamens. Illegitimate union : 3 : 0 : 0.

Short-styled by both pollens mixed together, of own-form longest and mid-length stamens. Illegitimate union: 13 : 0 : 0.

Short-styled by pollen of longest stamens of mid-styled. Illegitimate union : 7 : 0 : 0.

Short-styled by pollen of mid-length stamens of long-styled. Illegitimate union: 10 : 1 : 54.

We here see that thirty-six flowers on the three forms legitimately fertilised yielded 30 capsules, these containing on an average 58.36 seeds. Ninety-five flowers illegitimately fertilised yielded 12 capsules, containing on an average 28.58 seeds. Therefore the fertility of the six legitimate to that of the twelve illegitimate unions, as judged by the proportion of flowers which yielded capsules, is as 100 to 15, and judged by the average number of seeds per capsule as 100 to 49. This plant, in comparison with the two South American species previously described, produces many more seeds, and the illegitimately fertilised flowers are not quite so sterile.

Oxalis rosea.

Hildebrand possessed in a living state only the long-styled form of this trimorphic Chilian species. (4/14. 'Monatsber. der Akad. der Wiss. Berlin' 1866 page 372.) The pollen-grains from the two sets of anthers differ in diameter as 9 to 7.5, or as 100 to 83. He has further shown that there is an analogous difference between the grains from the two sets of anthers of the same flower in five other species of Oxalis, besides those already described. The present species differs remarkably from the long-styled form of the three species previously experimented on, in a much larger proportion of the flowers setting capsules when fertilised with their own-form pollen. Hildebrand fertilised 60 flowers with pollen from the mid-length stamens (of either the same or another flower), and they yielded no less than 55 capsules, or 92 per cent. These capsules contained on an average 5.62 seeds; but we have no means of judging how near an approach this average makes to that from flowers legitimately fertilised. He also fertilised 45 flowers with pollen from the shortest stamens, and these yielded only 17 capsules, or 31 per cent, containing on an average only 2.65 seeds. We thus see that about thrice as many flowers, when fertilised with pollen from the mid-length stamens, produced capsules, and these contained twice as many seeds, as did the flowers fertilised with pollen from the shortest stamens. It thus appears (and we find some evidence of the same fact with O. speciosa), that the same rule holds good with Oxalis as with Lythrum salicaria; namely, that in any two unions, the greater the inequality in length between the pistils and stamens, or, which is the same thing, the greater the distance of the stigma from the anthers, the pollen of which is used for fertilisation, the less fertile is the union,—whether judged by the proportion of flowers which set capsules, or by the average number of seeds per capsule. The rule cannot be explained in this case any more than in that of Lythrum, by supposing that wherever there is greater liability to self-fertilisation, this is checked by the union being rendered more sterile; for exactly the reverse occurs, the liability to self-fertilisation being greatest in the unions between the pistils and stamens which approach each other the nearest, and these are the more fertile. I may add that I also possessed some long-styled plants of this species: one was covered by a net, and it set spontaneously a few capsules, though extremely few compared with those produced by a plant growing by itself, but exposed to the visits of bees.

With most of the species of Oxalis the short-styled form seems to be the most sterile of the three forms, when these are illegitimately fertilised; and I will add two other cases to those already given. I fertilised 29 short-styled flowers of O. compressa with pollen from their own two sets of stamens (the pollen- grains of which differ in diameter as 100 and 83), and not one produced a capsule. I formerly cultivated during several years the short-styled form of a species purchased under the name of O. Bowii (but I have some doubts whether it was rightly named), and fertilised many flowers with their own two kinds of pollen, which differ in diameter in the usual manner, but never got a single seed. On the other hand, Hildebrand says that the short-styled form of O. Deppei, growing by itself, yields plenty of seed; but it is not positively known that this species is heterostyled; and the pollen-grains from the two sets of anthers do not differ in diameter.

Some facts communicated to me by Fritz Muller afford excellent evidence of the utter sterility of one of the forms of certain trimorphic species of Oxalis, when growing isolated. He has seen in St. Catharina, in Brazil, a large field of young sugar-cane, many acres in extent, covered with the red blossoms of one form alone, and these did not produce a single seed. His own land is covered with the short-styled form of a white-flowered trimorphic species, and this is equally sterile; but when the three forms were planted near together in his garden they seeded freely. With two other trimorphic species he finds that isolated plants are always sterile.

Fritz Muller formerly believed that a species of Oxalis, which is so abundant in St. Catharina that it borders the roads for miles, was dimorphic instead of trimorphic. Although the pistils and stamens vary greatly in length, as was evident in some specimens sent to me, yet the plants can be divided into two sets, according to the lengths of these organs. A large proportion of the anthers are of a white colour and quite destitute of pollen; others which are pale yellow contain many bad with some good grains; and others again which are bright yellow have apparently sound pollen; but he has never succeeded in finding any fruit on this species. The stamens in some of the flowers are partially converted into petals. Fritz Muller after reading my description, hereafter to be given, of the illegitimate offspring of various heterostyled species, suspects that these plants of Oxalis may be the variable and sterile offspring of a single form of some trimorphic species, perhaps accidentally introduced into the district, which has since been propagated asexually. It is probable that this kind of propagation would be much aided by there being no expenditure in the production of seed.

Oxalis (Biophytum) sensitiva.

This plant is ranked by many botanists as a distinct genus. Mr. Thwaites sent me a number of flowers preserved in spirits from Ceylon, and they are clearly trimorphic. The style of the long-styled form is clothed with many scattered hairs, both simple and glandular; such hairs are much fewer on the style of the mid-styled, and quite absent from that of the short-styled form; so that this plant resembles in this respect O. Valdiviana and Regnelli. Calling the length of the two lobes of the stigma of the long-styled form 100, that of the mid- styled is 141, and that of the short-styled 164. In all other cases, in which the stigma in this genus differs in size in the three forms, the difference is of a reversed nature, the stigma of the long-styled being the largest, and that of the short-styled the smallest. The diameter of the pollen-grains from the longest stamens being represented by 100, those from the mid-length stamens are 91, and those from the shortest stamens 84 in diameter. This plant is remarkable, as we shall see in the last chapter of this volume, by producing long-styled, mid-styled, and short-styled cleistogamic flowers.

HOMOSTYLED SPECIES OF OXALIS.

Although the majority of the species in the large genus Oxalis seem to be trimorphic, some are homostyled, that is, exist under a single form; for instance the common O. acetosella, and according to Hildebrand two other widely distributed European species, O. stricta and corniculata. Fritz Muller also informs me that a similarly constituted species is found in St. Catharina, and that it is quite fertile with its own pollen when insects are excluded. The stigmas of O. stricta and of another homostyled species, namely O. tropaeoloides, commonly stand on a level with the upper anthers, and both these species are likewise quite fertile when insects are excluded.

With respect to O. acetosella, Hildebrand says that in all the many specimens examined by him the pistil exceeded the longer stamens in length. I procured 108 flowers from the same number of plants growing in three distant parts of England; of these 86 had their stigmas projecting considerably above, whilst 22 had them nearly on a level with the upper anthers. In one lot of 17 flowers from the same wood, the stigmas in every flower projected fully as much above the upper anthers as these stood above the lower anthers. So that these plants might fairly be compared with the long-styled form of a heterostyled species; and I at first thought that O. acetosella was trimorphic. But the case is one merely of great variability. The pollen-grains from the two sets of anthers, as observed by Hildebrand and myself, do not differ in diameter. I fertilised twelve flowers on several plants with pollen from a distinct plant, choosing those with pistils of a different length; and 10 of these (i.e. 83 per cent) produced capsules, which contained on an average 7.9 seeds. Fourteen flowers were fertilised with their own pollen, and 11 of these (i.e. 79 per cent) yielded capsules, containing a larger average of seed, namely 9.2. These plants, therefore, in function show not the least sign of being heterostyled. I may add that 18 flowers protected by a net were left to fertilise themselves, and only 10 of these (i.e. 55 per cent) yielded capsules, which contained on an average only 6.3 seeds. So that the access of insects, or artificial aid in placing pollen on the stigma, increases the fertility of the flowers; and I found that this applied especially to those having shorter pistils. It should be remembered that the flowers hang downwards, so that those with short pistils would be the least likely to receive their own pollen, unless they were aided in some manner.

Finally, as Hildebrand has remarked, there is no evidence that any of the heterostyled species of Oxalis are tending towards a dioecious condition, as Zuccarini and Lindley inferred from the differences in the reproductive organs of the three forms, the meaning of which they did not understand.

PONTEDERIA [SP.?] (PONTEDERIACEAE).

Fritz Muller found this aquatic plant, which is allied to the Liliaceae, growing in the greatest profusion on the banks of a river in Southern Brazil. (4/15. "Ueber den Trimorphismus der Pontederien" 'Jenaische Zeitschrift' etc. Band 6 1871 page 74.) But only two forms were found, the flowers of which include three long and three short stamens. The pistil of the long-styled form, in two dried flowers which were sent me, was in length as 100 to 32, and its stigma as 100 to 80, compared with the same organs in the short-styled form. The long-styled stigma projects considerably above the upper anthers of the same flower, and stands on a level with the upper ones of the short-styled form. In the latter the stigma is seated beneath both its own sets of anthers, and is on a level with the anthers of the shorter stamens in the long-styled form. The anthers of the longer stamens of the short-styled form are to those of the shorter stamens of the long-styled form as 100 to 88 in length. The pollen-grains distended with water from the longer stamens of the short-styled form are to those from the shorter stamens of the same form as 100 to 87 in diameter, as deduced from ten measurements of each kind. We thus see that the organs in these two forms differ from one another and are arranged in an analogous manner, as in the long and short-styled forms of the trimorphic species of Lythrum and Oxalis. Moreover, the longer stamens of the long-styled form of Pontederia, and the shorter ones of the short-styled form are placed in a proper position for fertilising the stigma of a mid-styled form. But Fritz Muller, although he examined a vast number of plants, could never find one belonging to the mid-styled form. The older flowers of the long-styled and short-styled plants had set plenty of apparently good fruit; and this might have been expected, as they could legitimately fertilise one another. Although he could not find the mid-styled form of this species, he possessed plants of another species growing in his garden, and all these were mid-styled; and in this case the pollen-grains from the anthers of the longer stamens were to those from the shorter stamens of the same flower as 100 to 86 in diameter, as deduced from ten measurements of each kind. These mid-styled plants growing by themselves never produced a single fruit.

Considering these several facts, there can hardly be a doubt that both these species of Pontederia are heterostyled and trimorphic. This case is an interesting one, for no other Monocotyledonous plant is known to be heterostyled. Moreover, the flowers are irregular, and all other heterostyled plants have almost symmetrical flowers. The two forms differ somewhat in the colour of their corollas, that of the short-styled being of a darker blue, whilst that of the long-styled tends towards violet, and no other such case is known. Lastly, the three longer stamens alternate with the three shorter ones, whereas in Lythrum and Oxalis the long and short stamens belong to distinct whorls. With respect to the absence of the mid-styled form in the case of the Pontederia which grows wild in Southern Brazil, this would probably follow if only two forms had been originally introduced there; for, as we shall hereafter see from the observations of Hildebrand, Fritz Muller and myself, when one form of Oxalis is fertilised exclusively by either of the other two forms, the offspring generally belong to the two parent-forms.

Fritz Muller has recently discovered, as he informs me, a third species of Pontederia, with all three forms growing together in pools in the interior of S. Brazil; so that no shadow of doubt can any longer remain about this genus including trimorphic species. He sent me dried flowers of all three forms. In the long-styled form the stigma stands a little above the tips of the petals, and on a level with the anthers of the longest stamens in the other two forms. The pistil is in length to that of the mid-styled as 100 to 56, and to that of the short-styled as 100 to 16. Its summit is rectangularly bent upwards, and the stigma is rather broader than that of the mid-styled, and broader in about the ratio of 7 to 4 than that of the short-styled. In the mid-styled form, the stigma is placed rather above the middle of the corolla, and nearly on a level with the mid-length stamens in the other two forms; its summit is a little bent upwards. In the short-styled form the pistil is, as we have seen, very short, and differs from that in the other two forms in being straight. It stands rather beneath the level of the anthers of the shortest stamens in the long-styled and mid-styled forms. The three anthers of each set of stamens, more especially those of the shortest stamens, are placed one beneath the other, and the ends of the filaments are bowed a little upwards, so that the pollen from all the anthers would be effectively brushed off by the proboscis of a visiting insect. The relative diameters of the pollen-grains, after having been long soaked in water, are given in Table 4.d, as measured by my son Francis.

TABLE 4.d. Pontederia. Diameters of pollen-grains, after having been long soaked in water, in divisions of the micrometer.

Column 1: Source of Pollen-grains. Column 2: diameter.

Long-styled form, mid-length stamens (Average of 20 measurements): 13.2. Long-styled form, shortest stamens (10 measurements): 9.0.

Mid-styled form, longest stamens (15 measurements) : 16.4. Mid-styled form, shortest stamens (20 measurements): 9.1.

Short-styled form, longest stamens (20 measurements): 14.6. Short-styled form, mid-length stamens (20 measurements): 12.3.

We have here the usual rule of the grains from the longer stamens, the tubes of which have to penetrate the longer pistil, being larger than those from the stamens of less length. The extreme difference in diameter between the grains from the longest stamens of the mid-styled form, and from the shortest stamens of the long-styled, is as 16.4 to 9.0, or as 100 to 55; and this is the greatest difference observed by me in any heterostyled plant. It is a singular fact that the grains from the corresponding longest stamens in the two forms differ considerably in diameter; as do those in a lesser degree from the corresponding mid-length stamens in the two forms; whilst those from the corresponding shortest stamens in the long- and mid-styled forms are almost exactly equal. Their inequality in the two first cases depends on the grains in both sets of anthers in the short-styled form being smaller than those from the corresponding anthers in the other two forms; and here we have a case parallel with that of the mid-styled form of Lythrum salicaria. In this latter plant the pollen-grains of the mid-styled forms are of smaller size and have less fertilising power than the corresponding ones in the other two forms; whilst the ovarium, however fertilised, yields a greater number of seeds; so that the mid-styled form is altogether more feminine in nature than the other two forms. In the case of Pontederia, the ovarium includes only a single ovule, and what the meaning of the difference in size between the pollen-grains from the corresponding sets of anthers may be, I will not pretend to conjecture.

The clear evidence that the species just described is heterostyled and trimorphic is the more valuable as there is some doubt with respect to P. cordata, an inhabitant of the United States. Mr. Leggett suspects that it is either dimorphic or trimorphic, for the pollen-grains of the longer stamens are "more than twice the diameter or than eight times the mass of the grains of the shorter stamens. Though minute, these smaller grains seem as perfect as the larger ones." (4/16. 'Bulletin of the Torrey Botanical Club' 1875 volume 6 page 62.) On the other hand, he says that in all the mature flowers, "the style was as long at least as the longer stamens;" "whilst in the young flowers it was intermediate in length between the two sets of stamens;" and if this be so, the species can hardly be heterostyled.

CHAPTER V.

ILLEGITIMATE OFFSPRING OF HETEROSTYLED PLANTS.

Illegitimate offspring from all three forms of Lythrum salicaria. Their dwarfed stature and sterility, some utterly barren, some fertile. Oxalis, transmission of form to the legitimate and illegitimate seedlings. Primula Sinensis, Illegitimate offspring in some degree dwarfed and infertile. Equal-styled varieties of P. Sinensis, auricula, farinosa, and elatior. P. vulgaris, red-flowered variety, Illegitimate seedlings sterile. P. veris, Illegitimate plants raised during several successive generations, their dwarfed stature and sterility. Equal-styled varieties of P. veris. Transmission of form by Pulmonaria and Polygonum. Concluding remarks. Close parallelism between illegitimate fertilisation and hybridism.

We have hitherto treated of the fertility of the flowers of heterostyled plants, when legitimately and illegitimately fertilised. The present chapter will be devoted to the character of their offspring or seedlings. Those raised from legitimately fertilised seeds will be here called LEGITIMATE SEEDLINGS or PLANTS, and those from illegitimately fertilised seeds, ILLEGITIMATE SEEDLINGS or PLANTS. They differ chiefly in their degree of fertility, and in their powers of growth or vigour. I will begin with trimorphic plants, and I must remind the reader that each of the three forms can be fertilised in six different ways; so that all three together can be fertilised in eighteen different ways. For instance, a long-styled form can be fertilised legitimately by the longest stamens of the mid-styled and short-styled forms, and illegitimately by its own- form and mid-length and shortest stamens, also by the mid-length stamens of the mid-styled and by the shortest stamens of the short-styled form; so that the long-styled can be fertilised legitimately in two ways and illegitimately in four ways. The same holds good with respect to the mid-styled and short-styled forms. Therefore with trimorphic species six of the eighteen unions yield legitimate offspring, and twelve yield illegitimate offspring.

I will give the results of my experiments in detail, partly because the observations are extremely troublesome, and will not probably soon be repeated— thus, I was compelled to count under the microscope above 20,000 seeds of Lythrum salicaria—but chiefly because light is thus indirectly thrown on the important subject of hybridism.

Lythrum salicaria.

Of the twelve illegitimate unions two were completely barren, so that no seeds were obtained, and of course no seedlings could be raised. Seedlings were, however, raised from seven of the ten remaining illegitimate unions. Such illegitimate seedlings when in flower were generally allowed to be freely and legitimately fertilised, through the agency of bees, by other illegitimate plants belonging to the two other forms growing close by. This is the fairest plan, and was usually followed; but in several cases (which will always be stated) illegitimate plants were fertilised with pollen taken from legitimate plants belonging to the other two forms; and this, as might have been expected, increased their fertility. Lythrum salicaria is much affected in its fertility by the nature of the season; and to avoid error from this source, as far as possible, my observations were continued during several years. Some few experiments were tried in 1863. The summer of 1864 was too hot and dry, and, though the plants were copiously watered, some few apparently suffered in their fertility, whilst others were not in the least affected. The years 1865 and, especially, 1866, were highly favourable. Only a few observations were made during 1867. The results are arranged in classes according to the parentage of the plants. In each case the average number of seeds per capsule is given, generally taken from ten capsules, which, according to my experience, is a nearly sufficient number. The maximum number of seeds in any one capsule is also given; and this is a useful point of comparison with the normal standard—that is, with the number of seeds produced by legitimate plants legitimately fertilised. I will give likewise in each case the minimum number. When the maximum and minimum differ greatly, if no remark is made on the subject, it may be understood that the extremes are so closely connected by intermediate figures that the average is a fair one. Large capsules were always selected for counting, in order to avoid over-estimating the infertility of the several illegitimate plants.

In order to judge of the degree of inferiority in fertility of the several illegitimate plants, the following statement of the average and of the maximum number of seeds produced by ordinary or legitimate plants, when legitimately fertilised, some artificially and some naturally, will serve as a standard of comparison, and may in each case be referred to. But I give under each experiment the percentage of seeds produced by the illegitimate plants, in comparison with the standard legitimate number of the same form. For instance, ten capsules from the illegitimate long-styled plant (Number 10), which was legitimately and naturally fertilised by other illegitimate plants, contained on an average 44.2 seeds; whereas the capsules on legitimate long-styled plants, legitimately and naturally fertilised by other legitimate plants, contained on an average 93 seeds. Therefore this illegitimate plant yielded only 47 per cent of the full and normal complement of seeds.

STANDARD NUMBER OF SEEDS PRODUCED BY LEGITIMATE PLANTS OF THE THREE FORMS, WHEN LEGITIMATELY FERTILISED.

Long-styled form: Average number of seeds in each capsule, 93; Maximum number observed out of twenty-three capsules, 159.

Mid-styled form: Average number of seeds, 130; Maximum number observed out of thirty-one capsules, 151.

Short-styled form: Average number of seeds, 83.5; but we may, for the sake of brevity, say 83; Maximum number observed out of twenty-five capsules, 112.

CLASSES 1 AND 2. ILLEGITIMATE PLANTS RAISED FROM LONG-STYLED PARENTS FERTILISED WITH POLLEN FROM THE MID-LENGTH OR THE SHORTEST STAMENS OF OTHER PLANTS OF THE SAME FORM.

From this union I raised at different times three lots of illegitimate seedlings, amounting altogether to 56 plants. I must premise that, from not foreseeing the result, I did not keep a memorandum whether the eight plants of the first lot were the product of the mid-length or shortest stamens of the same form; but I have good reason to believe that they were the product of the latter. These eight plants were much more dwarfed, and much more sterile than those in the other two lots. The latter were raised from a long-styled plant growing quite isolated, and fertilised by the agency of bees with its own pollen; and it is almost certain, from the relative position of the organs of fructification, that the stigma under these circumstances would receive pollen from the mid-length stamens.

All the fifty-six plants in these three lots proved long-styled; now, if the parent-plants had been legitimately fertilised by pollen from the longest stamens of the mid-styled and short-styled forms, only about one-third of the seedlings would have been long-styled, the other two-thirds being mid-styled and short-styled. In some other trimorphic and dimorphic genera we shall find the same curious fact, namely, that the long-styled form, fertilised illegitimately by its own-form pollen, produces almost exclusively long-styled seedlings. (5/1. Hildebrand first called attention to this fact in the case of Primula Sinensis ('Botanische Zeitung' January 1, 1864 page 5); but his results were not nearly so uniform as mine.)

The eight plants of the first lot were of low stature: three which I measured attained, when fully grown, the heights of only 28, 29, and 47 inches; whilst legitimate plants growing close by were double this height, one being 77 inches. They all betrayed in their general appearance a weak constitution; they flowered rather later in the season, and at a later age than ordinary plants. Some did not flower every year; and one plant, behaving in an unprecedented manner, did not flower until three years old. In the two other lots none of the plants grew quite to their full and proper height, as could at once be seen by comparing them with the adjoining rows of legitimate plants. In several plants in all three lots, many of the anthers were either shrivelled or contained brown and tough, or pulpy matter, without any good pollen-grains, and they never shed their contents; they were in the state designated by Gartner as contabescent, which term I will for the future use. (5/2. 'Beitrage zur Kenntniss der Befruchtung' 1844 page 116.) In one flower all the anthers were contabescent excepting two which appeared to the naked eye sound; but under the microscope about two-thirds of the pollen-grains were seen to be small and shrivelled. In another plant, in which all the anthers appeared sound, many of the pollen- grains were shrivelled and of unequal sizes. I counted the seeds produced by seven plants (1 to 7) in the first lot of eight plants, probably the product of parents fertilised by their own-form shortest stamens, and the seeds produced by three plants in the other two lots, almost certainly the product of parents fertilised by their own-form mid-length stamens.

[PLANT 1.

This long-styled plant was allowed during 1863 to be freely and legitimately fertilised by an adjoining illegitimate mid-styled plant, but it did not yield a single seed-capsule. It was then removed and planted in a remote place close to a brother long-styled plant Number 2, so that it must have been freely though illegitimately fertilised; under these circumstances it did not yield during 1864 and 1865 a single capsule. I should here state that a legitimate or ordinary long-styled plant, when growing isolated, and freely though illegitimately fertilised by insects with its own pollen, yielded an immense number of capsules, which contained on an average 21.5 seeds.

PLANT 2.

This long-styled plant, after flowering during 1863 close to an illegitimate mid-styled plant, produced less than twenty capsules, which contained on an average between four and five seeds. When subsequently growing in company with Number 1, by which it will have been illegitimately fertilised, it yielded in 1866 not a single capsule, but in 1865 it yielded twenty-two capsules: the best of these, fifteen in number, were examined; eight contained no seed, and the remaining seven contained on an average only three seeds, and these seeds were so small and shrivelled that I doubt whether they would have germinated.

PLANTS 3 AND 4.

These two long-styled plants, after being freely and legitimately fertilised during 1863 by the same illegitimate mid-styled plant as in the last case, were as miserably sterile as Number 2.

PLANT 5.

This long-styled plant, after flowering in 1863 close to an illegitimate mid- styled plant, yielded only four capsules, which altogether included only five seeds. During 1864, 1865, and 1866, it was surrounded either by illegitimate or legitimate plants of the other two forms; but it did not yield a single capsule. It was a superfluous experiment, but I likewise artificially fertilised in a legitimate manner twelve flowers; but not one of these produced a capsule; so that this plant was almost absolutely barren.

PLANT 6.

This long-styled plant, after flowering during the favourable year of 1866, surrounded by illegitimate plants of the other two forms, did not produce a single capsule.

PLANT 7.

This long-styled plant was the most fertile of the eight plants of the first lot. During 1865 it was surrounded by illegitimate plants of various parentage, many of which were highly fertile, and must thus have been legitimately fertilised. It produced a good many capsules, ten of which yielded an average of 36.1 seeds, with a maximum of 47 and a minimum of 22; so that this plant produced 39 per cent of the full number of seeds. During 1864 it was surrounded by legitimate and illegitimate plants of the other two forms; and nine capsules (one poor one being rejected) yielded an average of 41.9 seeds, with a maximum of 56 and a minimum of 28; so that, under these favourable circumstances, this plant, the most fertile of the first lot, did not yield, when legitimately fertilised, quite 45 per cent of the full complement of seeds.]

In the second lot of plants in the present class, descended from the long-styled form, almost certainly fertilised with pollen from its own mid-length stamens, the plants, as already stated, were not nearly so dwarfed or so sterile as in the first lot. All produced plenty of capsules. I counted the number of seeds in only three plants, namely Numbers 8, 9, and 10.

[PLANT 8.

This plant was allowed to be freely fertilised in 1864 by legitimate and illegitimate plants of the other two forms, and ten capsules yielded on an average 41.1 seeds, with a maximum of 73 and a minimum of 11. Hence this plant produced only 44 per cent of the full complement of seeds.

PLANT 9.

This long-styled plant was allowed in 1865 to be freely fertilised by illegitimate plants of the other two forms, most of which were moderately fertile. Fifteen capsules yielded on an average 57.1 seeds, with a maximum of 86 and a minimum of 23. Hence the plant yielded 61 per cent of the full complement of seeds.

PLANT 10.

This long-styled plant was freely fertilised at the same time and in the same manner as the last. Ten capsules yielded an average of 44.2 seeds, with a maximum of 69 and a minimum of 25; hence this plant yielded 47 per cent of the full complement of seeds.]

The nineteen long-styled plants of the third lot, of the same parentage as the last lot, were treated differently; for they flowered during 1867 by themselves so that they must have been illegitimately fertilised by one another. It has already been stated that a legitimate long-styled plant, growing by itself and visited by insects, yielded an average of 21.5 seeds per capsule, with a maximum of 35; but, to judge fairly of its fertility, it ought to have been observed during successive seasons. We may also infer from analogy that, if several legitimate long-styled plants were to fertilise one another, the average number of seeds would be increased; but how much increased I do not know; hence I have no perfectly fair standard of comparison by which to judge of the fertility of the three following plants of the present lot, the seeds of which I counted.

[PLANT 11.

This long-styled plant produced a large crop of capsules, and in this respect was one of the most fertile of the whole lot of nineteen plants. But the average from ten capsules was only 35.9 seeds, with a maximum of 60 and a minimum of 8.

PLANT 12.

This long-styled plant produced very few capsules; and ten yielded an average of only 15.4 seeds, with a maximum of 30 and a minimum of 4.

PLANT 13.

This plant offers an anomalous case; it flowered profusely, yet produced very few capsules; but these contained numerous seeds. Ten capsules yielded an average of 71.9 seeds, with a maximum of 95 and a minimum of 29. Considering that this plant was illegitimate and illegitimately fertilised by its brother long-styled seedlings, the average and the maximum are so remarkably high that I cannot at all understand the case. We should remember that the average for a legitimate plant legitimately fertilised is 93 seeds.]

CLASS 3. ILLEGITIMATE PLANTS RAISED FROM A SHORT-STYLED PARENT FERTILISED WITH POLLEN FROM OWN-FORM MID-LENGTH STAMENS.

I raised from this union nine plants, of which eight were short-styled and one long-styled; so that there seems to be a strong tendency in this form to reproduce, when self-fertilised, the parent-form; but the tendency is not so strong as with the long-styled. These nine plants never attained the full height of legitimate plants growing close to them. The anthers were contabescent in many of the flowers on several plants.

[PLANT 14.

This short-styled plant was allowed during 1865 to be freely and legitimately fertilised by illegitimate plants descended from self-fertilised mid-, long- and short-styled plants. Fifteen capsules yielded an average of 28.3 seeds, with a maximum of 51 and a minimum of 11; hence this plant produced only 33 per cent of the proper number of seeds. The seeds themselves were small and irregular in shape. Although so sterile on the female side, none of the anthers were contabescent.

PLANT 15.

This short-styled plant, treated like the last during the same year, yielded an average, from fifteen capsules, of 27 seeds, with a maximum of 49 and a minimum of 7. But two poor capsules may be rejected, and then the average rises to 32.6, with the same maximum of 49 and a minimum of 20; so that this plant attained 38 per cent of the normal standard of fertility, and was rather more fertile than the last, yet many of the anthers were contabescent.

PLANT 16.

This short-styled plant, treated like the two last, yielded from ten capsules an average of 77.8 seeds, with a maximum of 97 and a minimum of 60; so that this plant produced 94 per cent of the full number of seeds.

PLANT 17.

This, the one long-styled plant of the same parentage as the last three plants, when freely and legitimately fertilised in the same manner as the last, yielded an average from ten capsules of 76.3 rather poor seeds, with a maximum of 88 and a minimum of 57. Hence this plant produced 82 per cent of the proper number of seeds. Twelve flowers enclosed in a net were artificially and legitimately fertilised with pollen from a legitimate short-styled plant; and nine capsules yielded an average of 82.5 seeds, with a maximum of 98 and a minimum of 51; so that its fertility was increased by the action of pollen from a legitimate plant, but still did not reach the normal standard.]

CLASS 4. ILLEGITIMATE PLANTS RAISED FROM A MID-STYLED PARENT FERTILISED WITH POLLEN FROM OWN-FORM LONGEST STAMENS.

After two trials, I succeeded in raising only four plants from this illegitimate union. These proved to be three mid-styled and one long-styled; but from so small a number we can hardly judge of the tendency in mid-styled plants when self-fertilised to reproduce the same form. These four plants never attained their full and normal height; the long-styled plant had several of its anthers contabescent.

[PLANT 18.

This mid-styled plant, when freely and legitimately fertilised during 1865 by illegitimate plants descended from self-fertilised long-, short-, and mid-styled plants, yielded an average from ten capsules of 102.6 seeds, with a maximum of 131 and a minimum of 63: hence this plant did not produce quite 80 per cent of the normal number of seeds. Twelve flowers were artificially and legitimately fertilised with pollen from a legitimate long-styled plant, and yielded from nine capsules an average of 116.1 seeds, which were finer than in the previous case, with a maximum of 135 and a minimum of 75; so that, as with Plant 17, pollen from a legitimate plant increased the fertility, but did not bring it up to the full standard.

PLANT 19.

This mid-styled plant, fertilised in the same manner and at the same period as the last, yielded an average from ten capsules of 73.4 seeds, with a maximum of 87 and a minimum of 64: hence this plant produced only 56 per cent of the full number of seeds. Thirteen flowers were artificially and legitimately fertilised with pollen from a legitimate long-styled plant, and yielded ten capsules with an average of 95.6 seeds; so that the application of pollen from a legitimate plant added, as in the two previous cases, to the fertility, but did not bring it up to the proper standard.

PLANT 20.

This long-styled plant, of the same parentage with the two last mid-styled plants, and freely fertilised in the same manner, yielded an average from ten capsules of 69.6 seeds, with a maximum of 83 and a minimum of 52: hence this plant produced 75 per cent of the full number of seeds.]

CLASS 5. ILLEGITIMATE PLANTS RAISED FROM A SHORT-STYLED PARENT FERTILISED WITH POLLEN FROM THE MID-LENGTH STAMENS OF THE LONG-STYLED FORM.

In the four previous classes, plants raised from the three forms fertilised with pollen from either the longer or shorter stamens of the same form, but generally not from the same plant, have been described. Six other illegitimate unions are possible, namely, between the three forms and the stamens in the other two forms which do not correspond in height with their pistils. But I succeeded in raising plants from only three of these six unions. From one of them, forming the present Class 5, twelve plants were raised; these consisted of eight short- styled, and four long-styled plants, with not one mid-styled. These twelve plants never attained quite their full and proper height, but by no means deserved to be called dwarfs. The anthers in some of the flowers were contabescent. One plant was remarkable from all the longer stamens in every flower and from many of the shorter ones having their anthers in this condition. The pollen of four other plants, in which none of the anthers were contabescent, was examined; in one a moderate number of grains were minute and shrivelled, but in the other three they appeared perfectly sound. With respect to the power of producing seed, five plants (Numbers 21 to 25) were observed: one yielded scarcely more than half the normal number; a second was slightly infertile; but the three others actually produced a larger average number of seeds, with a higher maximum, than the standard. In my concluding remarks I shall recur to this fact, which at first appears inexplicable.

[PLANT 21.

This short-styled plant, freely and legitimately fertilised during 1865 by illegitimate plants, descended from self-fertilised long-, mid- and short-styled parents, yielded an average from ten capsules of 43 seeds, with a maximum of 63 and a minimum of 26: hence this plant, which was the one with all its longer and many of its shorter stamens contabescent, produced only 52 per cent of the proper number of seeds.

PLANT 22.

This short-styled plant produced perfectly sound pollen, as viewed under the microscope. During 1866 it was freely and legitimately fertilised by other illegitimate plants belonging to the present and the following class, both of which include many highly fertile plants. Under these circumstances it yielded from eight capsules an average of 100.5 seeds, with a maximum of 123 and a minimum of 86; so that it produced 121 per cent of seeds in comparison with the normal standard. During 1864 it was allowed to be freely and legitimately fertilised by legitimate and illegitimate plants, and yielded an average, from eight capsules, of 104.2 seeds, with a maximum of 125 and a minimum of 90; consequently it exceeded the normal standard, producing 125 per cent of seeds. In this case, as in some previous cases, pollen from legitimate plants added in a small degree to the fertility of the plant; and the fertility would, perhaps, have been still greater had not the summer of 1864 been very hot and certainly unfavourable to some of the plants of Lythrum.

PLANT 23.

This short-styled plant produced perfectly sound pollen. During 1866 it was freely and legitimately fertilised by the other illegitimate plants specified under the last experiment, and eight capsules yielded an average of 113.5 seeds, with a maximum of 123 and a minimum of 93. Hence this plant exceeded the normal standard, producing no less than 136 per cent of seeds.

PLANT 24.

This long-styled plant produced pollen which seemed under the microscope sound; but some of the grains did not swell when placed in water. During 1864 it was legitimately fertilised by legitimate and illegitimate plants in the same manner as Plant 22, but yielded an average, from ten capsules, of only 55 seeds, with a maximum of 88 and a minimum of 24, thus attaining 59 per cent of the normal fertility. This low degree of fertility, I presume, was owing to the unfavourable season; for during 1866, when legitimately fertilised by illegitimate plants in the manner described under Number 22, it yielded an average, from eight capsules, of 82 seeds, with a maximum of 120 and a minimum of 67, thus producing 88 per cent of the normal number of seeds.

PLANT 25.

The pollen of this long-styled plant contained a moderate number of poor and shrivelled grains; and this is a surprising circumstance, as it yielded an extraordinary number of seeds. During 1866 it was freely and legitimately fertilised by illegitimate plants, as described under Number 22, and yielded an average, from eight capsules, of 122.5 seeds, with a maximum of 149 and a minimum of 84. Hence this plant exceeded the normal standard, producing no less than 131 per cent of seeds.]

CLASS 6. ILLEGITIMATE PLANTS RAISED FROM MID-STYLED PARENTS FERTILISED WITH POLLEN FROM THE SHORTEST STAMENS OF THE LONG-STYLED FORM.

I raised from this union twenty-five plants, which proved to be seventeen long- styled and eight mid-styled, but not one short-styled. None of these plants were in the least dwarfed. I examined, during the highly favourable season of 1866, the pollen of four plants: in one mid-styled plant, some of the anthers of the longest stamens were contabescent, but the pollen-grains in the other anthers were mostly sound, as they were in all the anthers of the shortest stamens; in two other mid-styled and in one long-styled plant many of the pollen-grains were small and shrivelled; and in the latter plant as many as a fifth or sixth part appeared to be in this state. I counted the seeds in five plants (Numbers 26 to 30), of which two were moderately sterile and three fully fertile.

[PLANT 26.

This mid-styled plant was freely and legitimately fertilised, during the rather unfavourable year 1864, by numerous surrounding legitimate and illegitimate plants. It yielded an average, from ten capsules, of 83.5 seeds, with a maximum of 110 and a minimum of 64, thus attaining 64 per cent of the normal fertility. During the highly favourable year 1866, it was freely and legitimately fertilised by illegitimate plants belonging to the present Class and to Class 5, and yielded an average, from eight capsules, of 86 seeds, with a maximum of 109 and a minimum of 61, and thus attained 66 per cent of the normal fertility. This was the plant with some of the anthers of the longest stamens contabescent as above mentioned.

PLANT 27.

This mid-styled plant, fertilised during 1864 in the same manner as the last, yielded an average, from ten capsules, of 99.4 seeds, with a maximum of 122 and a minimum of 53, thus attaining to 76 per cent of the normal fertility. If the season had been more favourable, its fertility would probably have been somewhat greater, but, judging from the last experiment, only in a slight degree.

PLANT 28.

This mid-styled plant, when legitimately fertilised during the favourable season of 1866, in the manner described under Number 26, yielded an average, from eight capsules, of 89 seeds, with a maximum of 119 and a minimum of 69, thus producing 68 per cent of the full number of seeds. In the pollen of both sets of anthers, nearly as many grains were small and shrivelled as sound.

PLANT 29.

This long-styled plant was legitimately fertilised during the unfavourable season of 1864, in the manner described under Number 26, and yielded an average, from ten capsules, of 84.6 seeds, with a maximum of 132 and a minimum of 47, thus attaining to 91 per cent of the normal fertility. During the highly favourable season of 1866, when fertilised in the manner described under Number 26, it yielded an average, from nine capsules (one poor capsule having been excluded), of 100 seeds, with a maximum of 121 and a minimum of 77. This plant thus exceeded the normal standard, and produced 107 per cent of seeds. In both sets of anthers there were a good many bad and shrivelled pollen-grains, but not so many as in the last-described plant.

Plant 30.

This long-styled plant was legitimately fertilised during 1866 in the manner described under Number 26, and yielded an average, from eight capsules, of 94 seeds, with a maximum of 106 and a minimum of 66; so that it exceeded the normal standard, yielding 101 per cent of seeds.

Plant 31.

Some flowers on this long-styled plant were artificially and legitimately fertilised by one of its brother illegitimate mid-styled plants; and five capsules yielded an average of 90.6 seeds, with a maximum of 97 and a minimum of 79. Hence, as far as can be judged from so few capsules, this plant attained, under these favourable circumstances, 98 per cent of the normal standard.]

CLASS 7. ILLEGITIMATE PLANTS RAISED FROM MID-STYLED PARENTS FERTILISED WITH POLLEN FROM THE LONGEST STAMENS OF THE SHORT-STYLED FORM.

It was shown in the last chapter that the union from which these illegitimate plants were raised is far more fertile than any other illegitimate union; for the mid-styled parent, when thus fertilised, yielded an average (all very poor capsules being excluded) of 102.8 seeds, with a maximum of 130; and the seedlings in the present class likewise have their fertility not at all lessened. Forty plants were raised; and these attained their full height and were covered with seed-capsules. Nor did I observe any contabescent anthers. It deserves, also, particular notice that these plants, differently from what occurred in any of the previous classes, consisted of all three forms, namely, eighteen short-styled, fourteen long-styled, and eight mid-styled plants. As these plants were so fertile, I counted the seeds only in the two following cases.

[PLANT 32.

This mid-styled plant was freely and legitimately fertilised during the unfavourable year of 1864, by numerous surrounding legitimate and illegitimate plants. Eight capsules yielded an average of 127.2 seeds, with a maximum of 144 and a minimum of 96; so that this plant attained 98 per cent of the normal standard.

PLANT 33.

This short-styled plant was fertilised in the same manner and at the same time with the last; and ten capsules yielded an average of 113.9, with a maximum of 137 and a minimum of 90. Hence this plant produced no less than 137 per cent of seeds in comparison with the normal standard.]

CONCLUDING REMARKS ON THE ILLEGITIMATE OFFSPRING OF THE THREE FORMS OF Lythrum salicaria.

From the three forms occurring in approximately equal numbers in a state of nature, and from the results of sowing seed naturally produced, there is reason to believe that each form, when legitimately fertilised, reproduces all three forms in about equal numbers. Now, we have seen (and the fact is a very singular one) that the fifty-six plants produced from the long-styled form, illegitimately fertilised with pollen from the same form (Class 1 and 2), were all long-styled. The short-styled form, when self-fertilised (Class 3), produced eight short-styled and one long-styled plant; and the mid-styled form, similarly treated (Class 4), produced three mid-styled and one long-styled offspring; so that these two forms, when illegitimately fertilised with pollen from the same form, evince a strong, but not exclusive, tendency to reproduce the parent-form. When the short-styled form was illegitimately fertilised by the long-styled form (Class 5), and again when the mid-styled was illegitimately fertilised by the long-styled (Class 6), in each case the two parent-forms alone were reproduced. As thirty-seven plants were raised from these two unions, we may, with much confidence, believe that it is the rule that plants thus derived usually consist of both parent-forms, but not of the third form. When, however, the mid-styled form was illegitimately fertilised by the longest stamens of the short-styled (Class 7), the same rule did not hold good; for the seedlings consisted of all three forms. The illegitimate union from which these latter seedlings were raised is, as previously stated, singularly fertile, and the seedlings themselves exhibited no signs of sterility and grew to their full height. From the consideration of these several facts, and from analogous ones to be given under Oxalis, it seems probable that in a state of nature the pistil of each form usually receives, through the agency of insects, pollen from the stamens of corresponding height from both the other forms. But the case last given shows that the application of two kinds of pollen is not indispensable for the production of all three forms. Hildebrand has suggested that the cause of all three forms being regularly and naturally reproduced, may be that some of the flowers are fertilised with one kind of pollen, and others on the same plant with the other kind of pollen. Finally, of the three forms, the long-styled evinces somewhat the strongest tendency to reappear amongst the offspring, whether both, or one, or neither of the parents are long-styled.

[TABLE 5.30. Tabulated results of the fertility of the foregoing illegitimate plants, when legitimately fertilised, generally by illegitimate plants, as described under each experiment. Plants 11, 12 and 13 are excluded, as they were illegitimately fertilised.

NORMAL STANDARD OF FERTILITY OF THE THREE FORMS, WHEN LEGITIMATELY AND NATURALLY FERTILISED.

Column 1: Form. Column 2: Average number of seeds per capsule. Column 3: Maximum number in any one capsule. Column 4: Minimum number in any one capsule.

Long-styled : 93 : 159 : No record was kept as all very poor capsules were rejected. Mid-styled : 130 : 151 : No record was kept as all very poor capsules were rejected. Short-styled : 83.5 : 112 : No record was kept as all very poor capsules were rejected.

TABLE 5.30. Continued.

CLASS 1 AND CLASS 2.—ILLEGITIMATE PLANTS RAISED FROM LONG-STYLED PARENTS FERTILISED WITH POLLEN FROM OWN-FORM MID-LENGTH OR SHORTEST STAMENS.

Column 1: Number (name) of plant. Column 2: Form. Column 3: Average number of seeds per capsule. Column 4: Maximum number of seeds in any one capsule. Column 5: Minimum number of seeds in any one capsule. Column 6: Average number of seeds, expressed as the percentage of the normal standard.

1 : Long-styled : 0 : 0 : 0 : 0. 2 : Long-styled : 4.5 : ? : 0 : 5. 3 : Long-styled : 4.5 : ? : 0 : 5. 4 : Long-styled : 4.5 : ? : 0 : 5. 5 : Long-styled : 0 or 1 : 2 : 0 : 0 or 1. 6 : Long-styled : 0 : 0 : 0 : 0. 7 : Long-styled : 36.1 : 47 : 22 : 39. 8 : Long-styled : 41.1 : 73 : 11 : 44. 9 : Long-styled : 57.1 : 86 : 23 : 61. 10 : Long-styled : 44.2 : 69 : 25 : 47.

CLASS 3. ILLEGITIMATE PLANTS RAISED FROM SHORT-STYLED PARENTS FERTILISED WITH POLLEN FROM OWN-FORM SHORTEST STAMENS.

14 : Short-styled : 28.3 : 51 : 11 : 33. 15 : Short-styled : 32.6 : 49 : 20 : 38. 16 : Short-styled : 77.8 : 97 : 60 : 94. 17 : Long-styled : 76.3 : 88 : 57 : 82.

CLASS 4. ILLEGITIMATE PLANTS RAISED FROM MID-STYLED PARENTS FERTILISED WITH POLLEN FROM OWN-FORM LONGEST STAMENS.

18 : Mid-styled : 102.6 : 131 : 63 : 80. 19 : Mid-styled : 73.4 : 87 : 64 : 56. 20 : Long-styled : 69.6 : 83 : 52 : 75.

CLASS 5. ILLEGITIMATE PLANTS RAISED FROM SHORT-STYLED PARENTS FERTILISED WITH POLLEN FROM THE MID-LENGTH STAMENS OF THE LONG-STYLED FORM.

21 : Short-styled : 43.0 : 63 : 26 : 52. 22 : Short-styled : 100.5 : 123 : 86 : 121. 23 : Short-styled : 113.5 : 123 : 93 : 136. 24 : Long-styled : 82.0 : 120 : 67 : 88. 25 : Long-styled : 122.5 : 149 : 84 : 131.

CLASS 6. ILLEGITIMATE PLANTS RAISED FROM MID-STYLED PARENTS FERTILISED WITH POLLEN FROM THE SHORTEST STAMENS OF THE LONG-STYLED FORM.

26 : Mid-styled : 86.0 : 109 : 61 : 66. 27 : Mid-styled : 99.4 : 122 : 53 : 76. 28 : Mid-styled : 89.0 : 119 : 69 : 68. 29 : Long-styled : 100.0 : 121 : 77 : 107. 30 : Long-styled : 94.0 : 106 : 66 : 101. 31 : Long-styled : 90.6 : 97 : 79 : 98.

CLASS 7. ILLEGITIMATE PLANTS RAISED FROM MID-STYLED PARENTS FERTILISED WITH POLLEN FROM THE LONGEST STAMENS OF THE SHORT-STYLED FORM.

32 : Mid-styled : 127.2 : 144 : 96 : 98. 33 : Short-styled : 113.9 : 137 : 90 : 137.

The lessened fertility of most of these illegitimate plants is in many respects a highly remarkable phenomenon. Thirty-three plants in the seven classes were subjected to various trials, and the seeds carefully counted. Some of them were artificially fertilised, but the far greater number were freely fertilised (and this is the better and natural plan) through the agency of insects, by other illegitimate plants. In the right hand, or percentage column, in Table 5.30, a wide difference in fertility between the plants in the first four and the last three classes may be perceived. In the first four classes the plants are descended from the three forms illegitimately fertilised with pollen taken from the same form, but only rarely from the same plant. It is necessary to observe this latter circumstance; for, as I have elsewhere shown, most plants, when fertilised with their own pollen, or that from the same plant, are in some degree sterile, and the seedlings raised from such unions are likewise in some degree sterile, dwarfed, and feeble. (5/3. 'The Effects of Cross and Self- fertilisation in the Vegetable Kingdom' 1876.) None of the nineteen illegitimate plants in the first four classes were completely fertile; one, however, was nearly so, yielding 96 per cent of the proper number of seeds. From this high degree of fertility we have many descending gradations, till we reach an absolute zero, when the plants, though bearing many flowers, did not produce, during successive years, a single seed or even seed-capsule. Some of the most sterile plants did not even yield a single seed when legitimately fertilised with pollen from legitimate plants. There is good reason to believe that the first seven plants in Class 1 and 2 were the offspring of a long-styled plant fertilised with pollen from its own-form shortest stamens, and these plants were the most sterile of all. The remaining plants in Class 1 and 2 were almost certainly the product of pollen from the mid-length stamens, and although very sterile, they were less so than the first set. None of the plants in the first four classes attained their full and proper stature; the first seven, which were the most sterile of all (as already stated), were by far the most dwarfed, several of them never reaching to half their proper height. These same plants did not flower at so early an age, or at so early a period in the season, as they ought to have done. The anthers in many of their flowers, and in the flowers of some other plants in the first six classes, were either contabescent or included numerous small and shrivelled pollen-grains. As the suspicion at one time occurred to me that the lessened fertility of the illegitimate plants might be due to the pollen alone having been affected, I may remark that this certainly was not the case; for several of them, when fertilised by sound pollen from legitimate plants, did not yield the full complement of seeds; hence it is certain that both the female and male reproductive organs were affected. In each of the seven classes, the plants, though descended from the same parents, sown at the same time and in the same soil, differed much in their average degree of fertility.

Turning now to the fifth, sixth, and seventh classes, and looking to the right hand column of Table 5.30, we find nearly as many plants with a percentage of seeds above the normal standard as beneath it. As with most plants the number of seeds produced varies much, it might be thought that the present case was one merely of variability. But this view must be rejected, as far as the less fertile plants in these three classes are concerned: first, because none of the plants in Class 5 attained their proper height, which shows that they were in some manner affected; and, secondly, because many of the plants in Classes 5 and 6 produced anthers which were either contabescent or included small and shrivelled pollen-grains. And as in these cases the male organs were manifestly deteriorated, it is by far the most probable conclusion that the female organs were in some cases likewise affected, and that this was the cause of the reduced number of seeds.

With respect to the six plants in these three classes which yielded a very high percentage of seeds, the thought naturally arises that the normal standard of fertility for the long-styled and short-styled forms (with which alone we are here concerned) may have been fixed too low, and that the six legitimate plants are merely fully fertile. The standard for the long-styled form was deduced by counting the seeds in twenty-three capsules, and for the short-styled form from twenty-five capsules. I do not pretend that this is a sufficient number of capsules for absolute accuracy; but my experience has led me to believe that a very fair result may thus be gained. As, however, the maximum number observed in the twenty-five capsules of the short-styled form was low, the standard in this case may possibly be not quite high enough. But it should be observed, in the case of the illegitimate plants, that in order to avoid over-estimating their infertility, ten very fine capsules were always selected; and the years 1865 and 1866, during which the plants in the three latter classes were experimented on, were highly favourable for seed-production. Now, if this plan of selecting very fine capsules during favourable seasons had been followed for obtaining the normal standards, instead of taking, during various seasons, the first capsules which came to hand, the standards would undoubtedly have been considerably higher; and thus the fact of the six foregoing plants appearing to yield an unnaturally high percentage of seeds may, perhaps, be explained. On this view, these plants are, in fact, merely fully fertile, and not fertile to an abnormal degree. Nevertheless, as characters of all kinds are liable to variation, especially with organisms unnaturally treated, and as in the four first and more sterile classes, the plants derived from the same parents and treated in the same manner, certainly did vary much in sterility, it is possible that certain plants in the latter and more fertile classes may have varied so as to have acquired an abnormal degree of fertility. But it should be noticed that, if my standards err in being too low, the sterility of all the many sterile plants in the several classes will have to be estimated by so much the higher. Finally, we see that the illegitimate plants in the four first classes are all more or less sterile, some being absolutely barren, with one alone almost completely fertile; in the three latter classes, some of the plants are moderately sterile, whilst others are fully fertile, or possibly fertile in excess.

The last point which need here be noticed is that, as far as the means of comparison serve, some degree of relationship generally exists between the infertility of the illegitimate union of the several parent-forms and that of their illegitimate offspring. Thus the two illegitimate unions, from which the plants in Classes 6 and 7 were derived, yielded a fair amount of seed, and only a few of these plants are in any degree sterile. On the other hand, the illegitimate unions between plants of the same form always yield very few seeds, and their seedlings are very sterile. Long-styled parent-plants when fertilised with pollen from their own-form shortest stamens, appear to be rather more sterile than when fertilised with their own-form mid-length stamens; and the seedlings from the former union were much more sterile than those from the latter union. In opposition to this relationship, short-styled plants illegitimately fertilised with pollen from the mid-length stamens of the long- styled form (Class 5) are very sterile; whereas some of the offspring raised from this union were far from being highly sterile. It may be added that there is a tolerably close parallelism in all the classes between the degree of sterility of the plants and their dwarfed stature. As previously stated, an illegitimate plant fertilised with pollen from a legitimate plant has its fertility slightly increased. The importance of the several foregoing conclusions will be apparent at the close of this chapter, when the illegitimate unions between the forms of the same species and their illegitimate offspring, are compared with the hybrid unions of distinct species and their hybrid offspring.

OXALIS.

No one has compared the legitimate and illegitimate offspring of any trimorphic species in this genus. Hildebrand sowed illegitimately fertilised seeds of Oxalis Valdiviana, but they did not germinate (5/4. 'Botanische Zeitung' 1871 page 433 footnote.); and this fact, as he remarks, supports my view that an illegitimate union resembles a hybrid one between two distinct species, for the seeds in this latter case are often incapable of germination.

[The following observations relate to the nature of the forms which appear among the legitimate seedlings of Oxalis Valdiviana. Hildebrand raised, as described in the paper just referred to, 211 seedlings from all six legitimate unions, and the three forms appeared among the offspring from each union. For instance, long-styled plants were legitimately fertilised with pollen from the longest stamens of the mid-styled form, and the seedlings consisted of 15 long-styled, 18 mid-styled, and 6 short-styled. We here see that a few short-styled plants were produced, though neither parent was short-styled; and so it was with the other legitimate unions. Out of the above 211 seedlings, 173 belonged to the same two forms as their parents, and only 38 belonged to the third form distinct from either parent. In the case of O. Regnelli, the result, as observed by Hildebrand, was nearly the same, but more striking: all the offspring from four of the legitimate unions consisted of the two parent-forms, whilst amongst the seedlings from the other two legitimate unions the third form appeared. Thus, of the 43 seedlings from the six legitimate unions, 35 belonged to the same two forms as their parents, and only 8 to the third form. Fritz Muller also raised in Brazil seedlings from long-styled plants of O. Regnelli legitimately fertilised with pollen from the longest stamens of the mid-styled form, and all these belonged to the two parent-forms. (5/5. 'Jenaische Zeitschrift' etc. Band 6 1871 page 75.) Lastly, seedlings were raised by me from long-styled plants of O. speciosa legitimately fertilised by the short-styled form, and from the latter reciprocally fertilised by the long-styled; and these consisted of 33 long-styled and 26 short-styled plants, with not one mid-styled form. There can, therefore, be no doubt that the legitimate offspring from any two forms of Oxalis tend to belong to the same two forms as their parents; but that a few seedlings belonging to the third form occasionally make their appearance; and this latter fact, as Hildebrand remarks, may be attributed to atavism, as some of their progenitors will almost certainly have belonged to the third form.

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