In effecting the cross-fertilization of one of the younger flowers its eyes are again brought into contact with this second pair of discs, and these, with their pollen clubs, are in turn withdrawn, at length perhaps resulting in such a plastering of the insect's eyes as might seriously impair its vision, were it not fortunately of the compound sort.
In another allied example of the orchids—the Showy Orchid—we have, however, what would appear a clear adaptation to the head of a bee, though one which might also avail of the service of an occasional butterfly. A group of this beautiful species is shown in my illustration. A favored haunt is the dark damp woods, especially beneath hemlocks, and with its deep pink hood and pure white lip is quite showy enough to warrant its specific title, "spectabilis." An enlarged view of the blossom is seen in Fig. 7, and in Fig. 8 a still greater enlargement of the column.
I have seen many specimens with the pollen masses withdrawn, and others with their stigmas well covered with the grains. Though I have never seen an insect at work upon it in its haunt, the whole form of the opening of the flower would seem to imply a bee, particularly a bumblebee. If we insert the point of a lead-pencil into this opening, thus imitating the entrance of a bee, its bevelled surface comes in contact with the viscid discs by the rupture of a veil of membrane, which has hitherto protected them. The discs adhere to the pencil, and are withdrawn upon it (Fig. 9). At first in upright position, they soon assume the forward inclination, as previously described. The nectary is about the length of a bumblebee's tongue, and is, moreover, so amply expanded at the throat below the stigma as to comfortably admit its wedge-shaped head. The three progressive diagrams (Fig. 10) indicate the result in the event of such a visit.
The pollen discs are here very close together, and are protected within a membraneous cup, in which they sit as in a socket. As the insect inserts his head at the opening (A) it is brought against this tender membrane, which ruptures and exposes the viscid glands of the pollen masses, which become instantly attached to the face or head, perhaps the eyes, of the burly visitor. As the insect retreats from the flower, one or both of the pollinia are withdrawn, as at B. Then immediately follows a downward movement, which exactly anticipates the position of the stigma, and as the bee enters the next flower the pollen clubs are forced against it (C), as in the previous example.
In the case of a smaller bee visiting the flower, the insect would find it necessary to creep further into the opening, and thus might bring its thorax against the pollen-glands. In either case the change of position in the pollinia would insure the same result.
We have thus seen adaptation to the thorax, the eyes, and the face in the three examples given. And the entrance of the flower in each instance is so formed as to insure the proper angle of approach for the insect for the accomplishment of the desired result. This direct approach, so necessary in many orchids, is insured by various devices—by the position of the lip upon which the insect must alight; by the narrowed entrance of the throat of the flower in front of the nectary; by a fissure in the centre of the lip, by which the tongue is conducted, etc.
Many other species allied to the above possess similar devices, with slight variations; and there is still another group whose structure is distinctly adjusted to the tongues of insects—adaptations not merely of position of pollen masses, but even to the extent of a special modification in the entrance to the flower and the shape of the sticky gland, by which it may more securely adhere to that sipping member.
In the common pretty Purple-fringed Orchid, whose dense cylindrical spikes of plumy blossoms occasionally empurple whole marshes, we have an arrangement quite similar to the H. orbicularis just described, with the exception that the pollen-pouches are almost parallel, and not noticeably spread at the base (Fig. 11). In this case the eyes of sipping butterflies occasionally get their decoration of a tiny golden club, but more frequently their tongues.
If, however, the butterfly should approach directly in front of the flower, as in a larger blossom he would be most apt to do, he might sip the nectar indefinitely and withdraw his tongue without bringing it in contact with the viscid pollen discs. But in the dense crowding of the flowers, over which the insect flutters indiscriminately, the approach is oftenest made obliquely, and thus the tongue brushes the disc on the side approached, and the pollen mass is withdrawn. But an examination of this orchid affords no pronounced evidence of any specific intention. There is no unmistakable sign to demonstrate which approach is preferred or designed by the flower, and this dependence on the insect's tongue or eye would seem to be left to chance.
In another closely allied species, however, we have a distinct provision which insures the proper approach of the tongue—one of many similar devices by which the tongue is conducted directly to one or the other of the pollen discs.
This is the Ragged Orchid, a near relative of the foregoing, H. psycodes, but far less fortunate in its attributes of beauty, its long scattered spike of greenish-white flowers being so inconspicuous in its sedgy haunt as often to conceal the fact of its frequency. Its individual flower is shown enlarged at Fig. 12—the lip here cut with a lacerated fringe (H. lacera). The pollen-pouches approach slightly at the base, directly opposite the nectary, where the two viscid pollen-glands stand on guard. Now were the opening of the nectary at this point unimpeded, the same condition would exist as in the H. psycodes—the tongue might be inserted between the pollen discs and withdrawn without touching them. But here comes the remarkable and very exceptional provision to make this contact a certainty—a suggestive structural feature of this flower of which I am surprised to find no mention either in our botanies or in the literature of cross-fertilization, so far as I am familiar with its bibliography. Even Dr. Gray's description of the fertilization device of this species makes no mention of this singular and very important feature. The nectary here, instead of being freely open, as in other orchids described, is abruptly closed at the central portion by a firm protuberance or palate, which projects downward from the base of the stigma, and closely meets the lip below.
The throat of the nectary, thus centrally divided, presents two small lateral openings, each of which, from the line of approach through the much-narrowed entrance of the flower, is thus brought directly beneath the waiting disc upon the same side. The structure is easily understood from the two diagrams Figs. 12 and 13, both of which are indexed.
The viscid pollen-gland is here very peculiarly formed, elongated and pointed at each end, and it is not until we witness the act of its removal on the tongue of the butterfly that we can fully appreciate its significance.
I have often seen butterflies at work upon this orchid, and have observed their tongues generously decorated with the glands and remnants of the pollen masses.
The series of diagrams (Fig. 14) will, I think, fully demonstrate how this blossom utilizes the butterfly. At A we see the insect sipping, its tongue now in contact with the elongated disc, which adheres to and clasps it. The withdrawal of the tongue (B) removes the pollen from its pouch. At C it is seen entirely free and upright, from which position it quickly assumes the new attitude shown at D. As the tongue is now inserted into the subsequent blossom this pollen mass is thrust against the stigma (E), and a few of the pollen grains are thus withheld upon its viscid surface as the insect departs (F).
In this orchid we thus find a distinct adaptation to the tongue of a moth or butterfly.
Another similar device for assuring the necessary side approach is seen in H. flava (Fig. 15), a yellowish spiked species, more or less common in swamps and rich alluvial haunts.
Professor Wood remarks, botanically, "The tubercle (or palate) of the lip is a remarkable character." But he, too, has failed to note the equally remarkable palate of the ragged orchid, just described, both provisions having the same purpose, the insurance of an oblique approach to the nectary. In H. flava this "tubercle," instead of depending from the throat, grows upward from the lip, and, as we look at the flower directly from the front, completely hides the opening to the nectary, and an insect is compelled to insert its tongue on one side, which direction causes it to pass directly beneath the pollen disc, as in H. lacera, and with the same result.
Of all our native orchids, at least in the northeastern United States, the Cypripedium, or Moccasin-Flower, is perhaps the general favorite, and certainly the most widely known. This is readily accounted for not only by its frequency, but by its conspicuousness. The term "moccasin-flower" is applied more or less indiscriminately to all species. The flower is also known as the ladies'-slipper, more specifically Venus's-slipper—as warranted by its generic botanical title—from a fancied resemblance in the form of the inflated lip, which is characteristic of the genus. We may readily infer that the fair goddess was not consulted at the christening.
There are six native species of the cypripedium in this Eastern region, varying in shape and in color—shades of white, yellow, crimson, and pink. The mechanism of their cross-fertilization is the same in all, with only slight modifications.
The most common of the group, the C. acaule, most widely known as the moccasin-flower, whose large, nodding, pale crimson blooms we so irresistibly associate with the cool hemlock woods, will afford a good illustration.
The lip in all the cypripediums is more or less sac-like and inflated. In the present species, C. acaule, however, we see a unique variation, this portion of the flower being conspicuously bag-like, and cleft by a fissure down its entire anterior face. In Fig. 16 is shown a front view of the blossom, showing this fissure. The "column" (B) in the cypripedium is very distinctive, and from the front view is very non-committal. It is only as we see it in side section, or from beneath, that we fully comprehend the disposition of stigma and pollen. Upon the stalk of this column there appear from the front three lobes—two small ones at the sides, each of which hides an anther attached to its under face—the large terminal third lobe being in truth a barren rudiment of a former stamen, and which now overarches the stigma. The relative position of these parts may be seen in the under view.
The anthers in this genus, then, are two, instead of the previous single anther with its two pollen-cells. The pollen is also quite different in its character, being here in the form of a pasty mass, whose entire exposed surface, as the anther opens, is coated with a very viscid gluten.
With the several figures illustrating the cross-fertilization, the reader will readily anticipate any description of the process, and only a brief commentary will be required in my text.
I have repeatedly examined the flowers of C. acaule in their haunts, have observed groups wherein every flower still retained its pollen, others where one or both pollen masses had been withdrawn, and in several instances associated with them I have observed the inflated lip most outrageously bruised, torn, and battered, and occasionally perforated by a large hole. I had observed these facts in boyhood. The inference, of course, was that some insect had been guilty of the mutilation; but not until I read Darwin's description of the cross-fertilization of this species did I realize the full significance of these telltale evidences of the escape of the imprisoned insect. Since that time, many years ago, I have often sat long and patiently in the haunt of the cypripedium awaiting a natural demonstration of its cross-fertilization, but as yet no insect has rewarded my devotion.
At length, in hopelessness of reward by such means, I determined to see the process by more prosaic methods. Gathering a cluster of the freshly opened flowers, which still retained their pollen, I took them to my studio. I then captured a bumblebee, and forcibly persuaded him to enact the demonstration which I had so long waited for him peaceably to fulfil. Taking him by the wings, I pushed him into the fissure by which he is naturally supposed to enter without persuasion. He was soon within the sac, and the inflexed wings of the margin had closed above him, as shown in section, Fig. 17. He is now enclosed in a luminous prison, and his buzzing protests are audible and his vehemence visible from the outside of the sac. Let us suppose that he at length has become reconciled to his condition, and has determined to rationally fulfil the ideal of his environment, as he may perhaps have already done voluntarily before. The buzzing ceases, and our bee is now finding sweet solace for his incarceration in the copious nectar which he finds secreted among the fringy hairs in the upper narrowed portion of the flower, as shown at Fig. 18 A. Having satiated his appetite, he concludes to quit his close quarters. After a few moments of more vehement futile struggling and buzzing, he at length espies, through the passage above the nectary fringe, a gleaming light, as from two windows (A). Towards these he now approaches. As he advances the passage becomes narrower and narrower, until at length his back is brought against the overhanging stigma (Fig. 18 B). So narrow is the pass at this point that the efforts of the bee are distinctly manifest from the outside in the distension of the part and the consequent slight change in the droop of the lip. In another moment he has passed this ordeal, and his head is seen protruding from the window-like opening (A) on one side of the column. But his struggles are not yet ended, for his egress is still slightly checked by the narrow dimensions of the opening, and also by the detention of the anther, which his thorax has now encountered. A strange etiquette this of the cypripedium, which speeds its parting guest with a sticky plaster smeared all over its back. As the insect works its way beneath the viscid contact, the anther is seen to be drawn outward upon its hinge, and its yellow contents are spread upon the insect's back (Fig. 18 C), verily like a plaster. Catching our bee before he has a chance to escape with his generous floral compliments, we unceremoniously introduce him into another cypripedium blossom, to which, if he were more obliging, he would naturally fly. He loses no time in profiting by his past experience, and is quickly creeping the gantlet, as it were, or braving the needle's eye of this narrow passage. His pollen-smeared thorax is soon crowding beneath the overhanging stigma again, whose forward-pointed papillae scrape off a portion of it (Fig. 18 B), thus insuring the cross-fertilizing of the flower, the bee receiving a fresh effusion of cypripedium compliments piled upon the first as he says "good-bye." It is doubtful whether in his natural life he ever fully effaces the telltale effects of this demonstrative au revoir.
Such, with slight modifications, is the plan evolved by the whole cypripedium tribe. Darwin mentions bees as the implied fertilizers, and doubtless many of the smaller bees do effect cross-fertilization in the smaller species. But the more ample passage in acaule would suggest the medium-sized Bombus as better adapted—as the experiment herewith pictured from my own experience many times would seem to verify, while a honey-bee introduced into the flower failed to fulfil the demonstration, emerging at the little doorway above without a sign of the cordial parting token.
Occasionally I suppose a fool bumblebee is entrapped within the petal bower and fails to find the proper exit, or it may be—much less a fool—having run the gantlet once too often, decides to escape the ordeal; hence the occasional mutilated blossom already described.
One of the most beautiful of our orchids, though its claims to admiration in this instance are chiefly confined to the foliage, is the common "Rattlesnake-Plantain," its prostrate rosettes of exquisitely white reticulated leaves carpeting many a nook in the shadows of the hemlocks, its dense spikes of yellowish-white blossoms signalling their welcome to the bees, and fully compensating in interest what they may lack in other attractive attributes.
The single flower is shown enlarged in Fig. 19—A, a young blossom, with analyses B and C, the latter indexed; D, an older blossom, with similar analyses (E and F). Both sorts are to be found upon every spike of bloom, as the inflorescence begins at the base and proceeds upward. As we look into the more open flower we observe a dark-colored speck, which, by analysis, proves to be the lid of the anther. This portion is further shown enlarged in Fig. 20, A. If we gently lift it with a pin, we disclose the pollen masses in the cavity (B) thus opened (C, profile section), the two pairs united to a common viscid gland at the base, this gland again secreted behind a veil of moist membrane, as also shown at B. This membrane is, moreover, very sensitive to the touch. Below the flattened tip of the column, and at a sharp inward angle, is the stigma. In the freshly opened flower (Fig. 19, A) the column inclines forward, bringing the anther low down, and its base directly opposite the V-shaped orifice in the lip, which also is quite firmly closed beneath the equally converging upper hood of the blossom. The entrance is thus much narrowed. If we insert a pin in this V-shaped entrance it comes in contact with the sensitive membrane below the anther, and it is immediately ruptured, as shown at Fig. 20, D. The sticky gland is brought into immediate contact, and clasps the pin, which, now being withdrawn, brings away the pollen, as in E and F. Thus it is naturally removed on the tongue of its sipping bee.
The further demonstration will be better shown by profile sections (Fig. 21). Nectar is secreted in the hollow of the lip indicated, somewhat as in the cypripedium. If we now imitate with a probe the habit of the insect and the action of its tongue, we may witness a beautiful contrivance for cross-fertilization. We will suppose the bee to be working at the top of the spike. He thrusts his tongue into the narrow opening (G). The membrane protecting the pollen-gland, thus surely touched, ruptures as described, and the exposed gland attaches itself to the tongue, being withdrawn as at H, and located on the insect's tongue, as in F, Fig. 20. The bee leaves this flower cluster and flies to another, upon which it will usually begin operation at the bottom. The flower thus first encountered is an old bloom, as in Fig. 19, D. Its sepals are more spreading, the lip slightly lowered, and the column so changed as to present the plane of the stigma, before out of sight, in such a new position as to invariably receive the pollen. The tongue of a bee entering this flower conveys the pollen directly against the stigmatic surface (I), which retains its disentangled fecundating grains, as at J, and the flower's functional adaptations are fulfilled.
In the allied Spiranthes, or "Lady's-Tresses," a somewhat similar mechanism prevails, by which fertilization is largely effected by the changed position or angle of the stigma plane.
And thus we might proceed through all the orchid genera, each new device, though based upon one of the foregoing plans, affording its new surprise in its special modification in adaptation to its insect sponsor—all these various shapes, folds of petals, positions, colors, the size, length, and thickness of nectary, the relative positions of pollen and stigma, embodying an expression of welcome to the insect with which its life is so marvellously linked. Occasionally this astounding affinity is faithful to a single species of insect, which thus becomes the sole sponsor of the blossom, without whose association the orchid would become extinct. A remarkable instance of this special adaptation is seen in the great Angraecum orchid of Madagascar, described by Darwin; and inasmuch as this species glorifies Darwin's faith in the truth of his theory, and marks a notable victory in the long battle for its supremacy, it affords an inspiring theme for my closing paragraphs.
Among the host of sceptics—and were they not legion?—who met this evolutionary and revolutionary theory with incredulity, not to say ridicule or worse, was one who thus challenged its author shortly after the appearance of his "Fertilization of Orchids," addressing Darwin from Madagascar substantially as follows: "Upon your theory of evolution through natural selection all the various contrasting structural features of the orchids have direct reference to some insect which shall best cross-fertilize them. If an orchid has a nectary one inch long, an insect's tongue of equivalent length is implied; a nectary six inches in length likewise implies a tongue six inches long. What have you to say in regard to an orchid which flourishes here in Madagascar possessing a long nectary as slender as a knitting-needle and eleven inches in length? On your hypothesis there must be a moth with a tongue eleven inches long, or this nectary would never have been elaborated."
Darwin's reply was magnificent in its proof of the sublime conviction of the truth of his belief: "The existence of an orchid with a slender nectary eleven inches in length, and with nectar secreted at its tip, is a conclusive demonstration of the existence of a moth with a tongue eleven inches in length, even though no such moth is known."
Many of us remember the ridicule which was heaped upon him for this apparently blind adherence to an untenable theory. But victory complete and demoralizing to his opponents awaited this oracular utterance when later a disciple of Darwin, led by the same spirit of faith and conviction, visited Madagascar, and was soon able to affirm that he had caught the moth, a huge sphinx-moth, and that its tongue measured eleven inches in length.
Here we see the prophecy of the existence of an unknown moth, founded on the form of a blossom. At that time the moth had not been actually seen at work on the orchid, but who shall question for a moment that had the flower been visited in its twilight or moonlight haunt the murmur of humming wings about the blossom's throat would have attested the presence of the flower's affinity, for without the kiss of this identical moth the Angraecum must become extinct. No other moth can fulfil the conditions necessary to its perpetuation. The floral adaptation is such that the moth must force its large head far into the opening of the blossom in order to reach the sweets in the long nectary. In so doing the pollen becomes attached to the base of the tongue, and is withdrawn as the insect leaves the flower, and is thrust against the stigma in the next blossom visited. This was clearly demonstrated by Darwin in specimens sent to him, by means of a probe of the presumable length and diameter of the moth's tongue. Shorter-tongued moths would fail to remove the pollen, and also to reach the nectar, and would thus soon learn to realize that they were not welcome.
The Angraecum also affords in this long pendent nectary a most lucid illustration of the present workings of natural selection. The normal length of that nectary should be about eleven inches, but in fact this length varies considerably in the flowers of different plants, this tendency to variation in all organic life being an essential and amply demonstrated postulate of the entire theory of natural selection. Let us suppose a flower whose nectary chances to be only six inches in length. The moth visits this flower, but the tip of its tongue reaches the nectar long before it can bring its head into the opening of the tube. This being a vital condition, the moth fails to withdraw the pollen; and inasmuch as the pollen is usually deposited close to the head of the moth, this flower would receive no pollen upon its stigma. This particular blossom would thus be both barren and sterile. None of its pollen would be carried to other stigmas, nor would it set a seed to perpetuate by inheritance its shorter nectary.
Again, let us suppose the variation of an extra long nectary, and the writer recently saw a number of these orchids with nectaries thirteen inches in length. The moth comes, and now must needs insert its head to the utmost into the opening of the flower. This would insure its fertilization by the pollen on the insect's tongue; and even though the sipper failed to reach the nectar, the pollen would be withdrawn upon the tongue, to be carried to other flowers, which might thus be expected to inherit from the paternal side the tendency to the longer nectary. The tendency towards the perpetuation of the short nectary is therefore stopped, while that of the longer nectary is insured.
The singular hospitality of our milkweed blossom is nowhere matched among Flora's minions, and would seem occasionally in need of supervision.
Just outside the door here at my country studio, almost in touch of its threshold, year after year there blooms a large clump of milkweed (Asclepias cornuta), and, what with the fragrance of its purple pompons and the murmurous music of its bees, its fortnight of bloom is not permitted to be forgotten for a moment. Only a moment ago a whiff of more than usual redolence from the open window at which I am sitting reminded me that the flowers were even now in the heyday of their prime, and the loud droning music betokened that the bees were making the most of their opportunities.
Yielding to the temptation, I was soon standing in the midst of the plants. The purple fragrant umbels of bloom hung close about me on all sides, each flower, with its five generous horns of plenty, drained over and over again by the eager sipping swarm.
But the July sun is one thing to a bee and quite another thing to me. I have lingered long enough, however, to witness again the beautiful reciprocity, and to realize anew, with awe and reverence, how divinely well the milkweed and the bee understand each other. After a brief search among the blossom clusters I return to my seclusion with a few interesting specimens, which may serve as a text here at my desk by the open window.
Two months hence an occasional silky messenger will float away from the glistening clouds about the open milkweed pods, but who ever thanks the bees of June for them? The flower is but a bright anticipation—an expression of hope in the being of the parent plant. It has but one mission. All its fragrance, all its nectar, all its beauty of form and hue are but means towards the consummation of the eternal edict of creation—"Increase and multiply." To that end we owe all the infinite forms, designs, tints, decorations, perfumes, mechanisms, and other seemingly inexplicable attributes. Its threshold must bear its own peculiar welcome to its insect, or perhaps to its humming-bird friend, or counterpart; its nectaries must both tempt and reward his coming, and its petals assist his comfortable tarrying.
Next to the floral orchids, the mechanism of our milkweed blossom is perhaps the most complex and remarkable, and illustrates as perfectly as any of the orchid examples given in Darwin's noble work the absolute divine intention of the dependence of a plant species upon the visits of an insect.
Our milkweed flower is a deeply planned contrivance to insure such an end. It fills the air with enticing fragrance. Its nectaries are stored with sweets, and I fancy each opening bud keenly alert with conscious solicitude for its affinity. Though many other flowers manage imperfectly to perpetuate their kind in the default of insect intervention, the milkweed, like most of the orchids, is helpless and incapable of such resource. Inclose this budded umbel in tarlatan gauze and it will bloom days after its fellow-blooms have fallen, anticipating its consummation, but no pods will be seen upon this cluster.
What a singular decree has Nature declared with reference to the milkweed! She says, in plainest terms, "Your pollen must be removed on the leg of an insect, preferably a bee, or your kind shall perish from the face of the earth." And what is the deep-laid plan by which this end is assured? My specimens here on the desk will disclose it all.
Here are two bees, a fly, and a beetle, each hanging dead by its legs from a flower, an extreme sacrificial penalty, which is singularly frequent, but which was certainly not exacted nor contemplated in the design of the flower. A careful search among almost any good-sized cluster of milkweeds will show us many such prisoners. As in all flowers, the pollen of the milkweed blossom must come in contact with its stigma before fruition is possible. In this peculiar family of plants, however, the pollen is distinct in character, and closely suggests the orchids in its consistency and disposition. The yellow powdery substance with which we are all familiar in ordinary flowers is here absent, the pollen being collected in two club-shaped or, more properly, spatula-shaped masses, linked in pairs at their slender prolonged tips, each of which terminates in a sticky disc-shaped appendage united in V-shape below. These pollen masses are concealed in pockets (B) around the cylindrical centre of the flower, the discs only being exposed at the surface, at five equidistant points around its rim, where they lie in wait for the first unwary foot that shall touch them. A glance at the two views of this central portion of the flower, as it appears through my magnifying-glass—the honey-horns and sepals having been removed—will, I think, indicate its peculiar anatomy or mechanism. No stigma is to be seen in the flower, the stigmatic surface which is to receive the pollen being concealed within five compartments, each of which is protected by a raised tent-like covering, cleft along its entire apex by a fine fissure (A). Outside of each of these, and entirely separated from the stigma in the cavity, lie the pollen masses within their pockets, each pair uniting at the rim below in V-shape, the union at the lower limit of the fissure.
With this more intimate knowledge of the floral anatomy, let us now visit our milkweed-plant and observe closely.
A bee alights upon the flower—the object of its visit being, of course, the sweets located in the five horn-shaped nectaries. In order to reach this nectar the insect must hang to the bulky blossom. Instantly, and almost of necessity, it would seem, one or more of the feet are seen to enter the upper opening of the fissure, and during the insect's movements are drawn through to the base. The foot is thus conducted directly between the two viscid discs, which immediately cling closer than a brother, and as the foot is finally withdrawn, the pollen is pulled from its cell. The member now released seeks a fresh hold, and the same result follows, the leg almost inevitably entering the fissure, and this time drawing in the pollen directly against the sticky stigmatic surface within. The five honey-horns have now been drained, and as our bee leaves the flower he is plainly detained by this too hearty "shake" or "grip" of his host, and quite commonly must exert a slight struggle to free himself. As the foot is thus forcibly torn away, the pollen mass is commonly scraped entirely off and retained within the fissure, or perhaps parts at the stalk, leaving the terminal disc clinging on the insect's leg. Occasionally, when more than one leg is entangled, the dangling blossom is tossed and swayed for several seconds by the vigorous pulling and buzzing, and a number of these temporary captives upon a single milkweed-plant are always to be seen.
Not unfrequently the mechanism so well adapted exceeds its functions and proves a veritable trap, as indicated in my specimens. I have found three dead bees thus entrapped in a single umbel of blossoms, having been exhausted in their struggles for escape; and a search among the flowers at any time will show the frequency of this fatality, the victims including gnats, flies, crane-flies, bugs, wasps, beetles, and small butterflies. In every instance this prisoner is found dangling by one or more legs, with the feet firmly held in the grip of the fissure.
Almost any bee which we may catch at random upon a milkweed gives perfect evidence of his surroundings, its toes being decorated with the tiny yellow tags, each successive flower giving and taking, exchanging compliments, as it were, with his fellows. Ordinarily this fringe can hardly prove more than an embarrassment; but we may frequently discern an individual here and there which for some reason has received more than his share of the milkweed's compliments. His legs are conspicuously fringed with the yellow tags. He rests with a discouraged air upon a neighboring leaf, while honey, and even wings, are seemingly forgotten in his efforts to scrape off the cumbersome handicap.
An interesting incident, apropos of our embarrassed bee, was narrated to me by the late Alphonso Wood, the noted botanist. He had received by mail from California a small box containing a hundred or more dead bees, accompanied by a letter. The writer, an old bee-keeper, had experience, and desired enlightenment and advice. The letter stated that his bees were "dying by thousands from the attacks of a peculiar fungus." The ground around the hive was littered with the victims in all stages of helplessness, and the dead insects were found everywhere at greater distances scattered around his premises. It needed only a casual glance at the encumbered insects to see the nature of the malady. They were laden two or three pairs deep, as it were, with the pollen masses of a milkweed. The botanist wrote immediately to his anxious correspondent, informing him, and suggesting as a remedy the discovery and destruction of the mischievous plants, which must be thriving somewhere in his neighborhood. A subsequent letter conveyed the thanks of the bee-keeper, stating that the milkweeds—a whole field of them—had been found and destroyed, and the trouble had immediately ceased. I am not aware that Mr. Wood ever ascertained the particular species of milkweed in this case. It is not probable that our Eastern species need ever seriously threaten the apiary, though unquestionably large numbers of bees are annually destroyed by its excessive hospitality. I have repeatedly found honey-bees dead beneath the plants, and my cabinet shows a specimen of a large bumblebee which had succumbed to its pollen burden, its feet, and even the hairs upon its body, being fringed deep with the tiny clubs—one of the many specimens which I have discovered as the "grist in the mill" of that wise spider which usually spreads his catch-all beneath the milkweeds.
* * * * *
Allied to the milkweed is another plant, the dogbane (Apocynum), which has a similar trick of entrapping its insect friends. Its drooping, fragrant, bell-shaped white flowers and long slender pods will help to recall it. But its method of capture is somewhat similar to the milkweed. The anthers are divided by a V-shaped cavity, into which the insect's tongue is guided as it is withdrawn from the flower, and into which it often becomes so tightly wedged as to render escape impossible. I have found small moths dangling by the tongue, as seen in the illustration below.
Agalena, house-spider, 7.
Alypia, grape-vine-moth, 160.
Andromeda (A. ligustrina), singular greeting to the bee, 126; interior arrangement of flower, 128; release of the pollen, 129.
Angraecum, orchid of Madagascar, with nectary eleven inches long, 219.
Ants, herding the aphides, 166; a model honey-farm, 167.
Aphides, plant-lice, founders of the feast, 165; herded by ants, 167.
Apocynum, dogbane, 236.
Aprophora, spume-bearer, 82.
Arethusa bulbosa, orchid, 175.
Argiope, field spider, 8.
Arum, wild: —Position of the anthers, 141; progressive stages of change, 142.
Asclepias cornuta, milkweed, 227.
Asilus, "robber-fly", 8.
Axell, a follower of Darwin, 116.
Bees: —The drone of, 5; a counterpart of clover; dependence of clover on, 117; manner of approach, 121; black-and-white banded, 126; approach to the blue-flag, 131; experiment with the bumblebee, 209; his escape from the flower, 210; manner of cross-fertilizing, 212; manner of conveying the pollen, 218; his difficulties with the milkweed flower, 233; the cumbersome handicap, 234; destroyed by the milkweed, 235.
Beetles (Cicindela), tiger, 68.
Birds: —Swifts, 5; robin, 5; vireo, 5, 45; indigo, 5; chat, 5, 40; oriole, 5, 32; red-headed chippy; barn-swallow, 6, 28, 39, 40; cuckoo, 23; "kow-bird"; cow black-bird; bunting, 27; song-sparrow, 30, 40; Maryland yellow-throat, 28, 45; Wilson's thrush; chewink, 32; fly-catcher; bluebird; oven-bird; cat-bird; phoebe, 40; bobolink; "reed-bird," 53; humming, 227.
Birds' nests: —Flimsy structure of the cuckoo's, 26; song-sparrow's, 30; oriole's swinging hammock; cobweb structure of the vireo's, 32; size of yellow-bird's; summer yellow-bird's beautiful home, 47; a four-story house, a possible fashion in featherdom, 51; pipit's, 35; wood-sparrow's, 37.
Bittersweet (Celastrus scandens), queer little harlequins on, 9; its scarlet-coated seeds, 88.
Blackburn, Mrs., quoted, 35.
Blair, Patrick, his claims concerning pollen, 111.
Blossom ceremonies, 119.
Blue-flag, its hidden anthers reached only by the bumblebee or large fly,129; manner of the bee's approach, 131.
Burroughs on wren-building, 17.
Butterflies: —Great yellow swallow-tail (Papilio turnus); red admiral (Pyrameis Atlanta); small yellow (Philodice); semicolon (Grapta interrogationis); comma (Vanessa comma), 153; orange; white (Aphrodite), 154; white cabbage (Pontia oleracea) 153.
Cactus, prickly-pear, its golden bower, 118.
Collinsonia, horse-balm, 136.
Caterpillars, 10, 14, 15, 62.
Celastrus scandens, bittersweet, 88.
Chamaelirium luteum, devil's-bit, 133.
Cicada, victim of the sand-hornet, 77; manner of depositing its eggs; period of transformation, 97; time of hatching, 100.
Cicindela, tiger-beetle, 68.
Clover, cause of failure of crop in Australia, 117.
Cobwebs: —A dusty prize; a two year's span, 7; a mixed assortment in, 8.
Cone-flower (Rudbeckia hirta), 138; embryo seeds; arrangement of the anthers, 139.
Cow black-bird, 27; his favorite perch; old dame's theory, 28; an unwelcome intruder, 30; a prowling foe, 31.
Cow-bird: —Ravenous young parasite, 31; a clamoring lubber, 37; "Black Douglas" of the bird-home, 38; selected victims, 39; distribution of its eggs; vicious habits, 40; egg-laying intervals; demoralizing conditions; American species an improvement, 41; survival of the fittest, 42; balance of power, 44; outwitted, 51; massing for migration, 52.
Cross-fertilization, 115, 122, 178, 189, 194.
Cuckoos: —Poetic misnomer, 23; outrage on maternal affection; yellow-billed; black-billed; imagination versus facts, 25; bad workmanship of nest, 26; its stammering cry, 27; manner of depositing its eggs; handling the egg with her bill, 33; short period of incubation; voracious appetite of the young; aggressive selfishness, 34; the tragedy of the nest, 35; manner of disposing of its nest-mates, 36.
Cypripedium acaule, moccasin-flower; ladies'-slipper; Venus's-slipper, 205.
Darwin: —Process of anatomical evolution, 35; theory of cross-fertilization, 105; inspired insight, 115; his disciples, 116; experiments with pollen, 126; weakness of self-fertilizing flowers, 144; triumphant revelation, 171; reaffirming Sprengel's theory, 178; a chosen interpreter, 181; dependence on insects, 183; revealing the hidden treasure, 185; foretelling the manner of cross-fertilization, 189; description of the cross-fertilization, 209; bees as implied fertilizers, 212; truth of his belief, 220.
Darning-needle, dragon-fly (Libellulidae), 156; his dainty morsel, 160.
Delpino, a follower of Darwin, 116.
Desmodium, its hospitable welcome, 118.
Devil's-bit (Chamaelirium luteum), 133.
Digger wasp, its color and wire-like waist, 72; manner of working, 74; covering its tracks; opening the tomb, 76; living food for the young grub, 77; its remarkable carrying power, 78.
Dogbane (Apocynum), its fragrant, bell-shaped flowers, 236; trapping moths, 237.
Door-Step Neighbors: —Chronicle of a day, 58; disappearing holes, 59, 16; "ant-holes"; a danger signal; an unhealthy court, 61; a transformation, 62; an experiment; method of excavation, 63; a stalwart worker, 64; an uncouth nondescript; spider-like legs, 66; crawls on his back, 67; a tiny black wasp; a spider-catcher, 69; resting on her wings; inspecting her burrow, 70; manner of burying her prey; skilful workmanship, 71; a new-comer; her wire-like waist; digging her tunnel, 72; manner of working; sound of labor, 74; covering her tracks; opening the tomb, 76; fresh living food, 77; carrying seven times its weight; peculiar features of stone-piling, 78; color of the wasp, 79; the spume-bearer, 81; nomadic blossoms; a sack bearer, 83; winter quarters, 84.
Epeira, field spider, 8.
Epiphytes, air-plants, 181.
Evening primrose, its golden necklace, 118.
"Fertilization of Flowers," 116; wrong theory, 114.
Fertilization of orchids, 105, 183.
Flies: —Robber, 8; bluebottle, 8; harvest ichneumon, 45, 77, 96.
Foxes, wild gambols of, 6.
Froghopper. See Spume-bearer (Aprophora), 82.
Gaertner, recognizing the theory of cross-fertilization, 115.
Genesta, its reception of insects, 118.
Geranium, wild (G. sylvaticum), 112.
Gilbert, concerning cuckoo's eggs, 25.
Gray, Asa: —Demonstration concerning orchids, 184; surmise concerning the withdrawal of pollen, 188; orchid structure, 190.
Grew, Nehemias, discovery concerning pollen, 110; discoveries about pollen, 113; first step in progress, 116.
Habenaria flava: —Yellow-spiked, 203; H. lacera, ragged, 200; H. orbicularis, showy, 194, 199; H. psycodes, purple-fringed, 200; H. mascula, 189.
Heath, its distinguishing characteristics, 123.
Hemiptera, bugs with sucking beaks, 81.
Herbert: —A follower of Sprengel, 108; recognizing the principle of cross-fertilization, 115.
"Honey-dew Picnic": —Gathering of the clans, 153; a selected spot, 154; a motley assemblage, 155; an outlaw, 157; a finish fight, 158; funeral baked meats, 164; gathering his grist; the founder of the feast, 158.
Honey-guides, 112, 129.
Hornets: —Its heavy load, 9; on the watch, 15; "solitary," 17; queer home of, 18; great sand, 77; black paper, 161.
Horse-balm (Collinsonia), its singular shape, 136; manner of bee's approach to, 138.
Huber: —On insect slavery, 151; on the cultivation of the aphides, 166.
Insect Fertilization, 115.
Jack-in-the-Pulpit, detaining its guests, 119.
Jardine, Sir William, concerning cuckoo's eggs, 32.
Jenner, Dr., habits of the young cuckoo, 35.
Knight, Andrew: —On the divination of flowers, 108; theory of cross-fertilization, 115.
Koehlreuter: —Recognizing Sprengel's principles, 108; a botanical pioneer, 115.
Krunitz, on flower honey, 111.
Labiates, flowers with lips, 122.
Ladies'-tresses (Spiranthes), 218.
Larva: —Hornet, 16; "puss-moth," 76; psychid, 83.
Linnaeus: —Settling the theory of fertilization, 110; puzzled as to the function of honey, 111; a second step, 116; imperfect knowledge of the orchid, 173.
Logan, concerning the cuckoo, 23.
Lubbock: —On the divination of flowers, 108; follower of Darwin, 116; on the cultivation of aphides, 166.
Martial Spirit of Vespa, 19.
Membracis binotata, insect with a sharp beak, a tree-hopper, 91.
Milkweed: —Its matchless hospitality; purple pompons; its five horns, 227; its one mission; the humming-bird its friend, 228; complex mechanism; enticing fragrance; removal of pollen on insects' legs, 229; four captives, 230; its honey trap; its tenacious grip, 233; an assortment of victims; cumbersome handicap, 234; a wholesale destroyer, 235.
Mint family, 122.
Mnio-tiltidae, summer yellow-bird, 47.
Moccasin-flower (Cypripedium acaule), 205.
Moths: —Twilight; sphinx, 118, 190, 220; grape-vine, 160.
Mountain laurel: —Showers of pollen of; curious construction of flower of; withers if brought indoors, 124; character of the pollen, 125.
Mouse, motley collection of food of; mischief of, 7.
Mueller, Hermann: —On the divination of flowers, 108; on defective observation, 114; the relations between the flower and insect, 116; on fertilization, 142
Nature's Equilibrium, 39.
Natural observation, 57.
Nomadic blossoms, 83.
Orchids: —Dependence on insects, 144; strange mechanical adaptation; sweet-pogonia; perfume suggesting raspberries, 145; intention of the blossom, 146; adaptation for insects, 147; its fragrance a perfumed whisper of welcome, 148; a contrast, 172; form of invitation, 173; insect complement, 174; Arethusa bulbosa, 175; theories concerning the conveyance of the pollen, 176; the most highly specialized form of flowers, 180; distinguished by its structure; American varieties not air-plants; form of flower, 181; elasticity of the pollen of the Spectabilis, 182; self-fertilizing, 183; American and exotic species, 184; Arethusa's fragrance, 185; its structure, 186; significant depth of nectar wells; conditions demanded of insects, 187; Gray's surmise, 188; sphinx-moth its only complement, 190; manner of carrying the pollen by sphinx-moth, 193; extracting the pollen with a pencil; length of the nectary, 196; purple-fringed, 198; ragged, 200; very exceptional provision, 201; yellow-spiked, 203; moccasin-flower; ladies'-slipper; Venus's-slipper; the color of, 205; distinctive character of, 206; practical experiment, 209; imprisonment of the bee; manner of its release, 210; rattlesnake-plantain, 213; Angraecum, its long nectary, 219; tongue of a sphinx-moth eleven inches long, 220; nectary thirteen inches long, 223.
"Origin of Species": —First important presentation of the theory of cross-fertilization, 105; tardy appreciation of the work, 115.
Odynerus flavipes, wren-wasp, 10.
Ovid, concerning hornets, 18.
Parallels in Nature, 152.
Platanthera, orchid group, 192.
Pogonia ophioglossoides, sweet-pogonia, 145.
Polistes, brown wasp, 161.
Primrose, evening, 118.
Psychid: —A sack-bearer; drags its house with it; feeds on seed-pods, 83; winter quarters of silk, 84.
Queer Little Family: —Tree-hopper (Membracis binotata); a singular entertainment; graceful curves, 87; a branch in masquerade; queer thorns, 88; a sudden disappearance; animated thorns; like a covey of quails, 89; like "Bob White," 90; singular agility; queer anatomy; always ready for flight, 91; fondness for locust and oak-trees, simulating the color and character of the branches, 92; manner of sitting on the branches, 93; always headed towards the top; tiny tufts of cotton, 94; color and size of the tufts; a mere frothy shell; a riddle, 95; its relations, 96; an investigation, 97; its technique, 98; aerated cement; froth-house builder, 99; period of hatching, 100; a house for the winter; not a wanderer, 101.
Ragged Orchid (H. lacera), 200.
Rudbeckia hirta, cone-flower, 138.
Sage (Salvia officinalis), strange curved stamen, 119; nature's arrangement, 112.
Salvia, its welcome to the bee, 117.
Showy orchid (H. orbicularis),194.
Snorting war-horse, 18.
Solitude, the pleasures of, 3.
"Solomon's ant," 152.
Spectabilis, orchid, 182; its favorite haunt, 195.
Spiders, agalena, epeira, argiope, 8; a two years' span, 7; a silken vortex; miscellaneous food, 8.
Spiranthes, "Lady's-tresses," 218.
Sprengel, Christian Conrad: —Inspiration from the wild geranium, 108; on the mystery of color, 112; theory of fertilization; a poser to Linnaeus, 113; his wrong theory, 114; divining half the truth, 176; assumption disproved, 178.
Spume-bearer (Aprophora), its domicile of suds; wonderful power of jumping, 82.
Starling, dispossessing woodpecker from nest, 43.
Studio Company: —"Tumultuous privacy"; contested territory; snickering squirrels, 4; selected food; unsymmetrical carpentry; drone of bees; carol of birds; flurry of swifts; accompaniments to my toil, 5; wild fox; pet chipmonk; pet toad; his lightning tongue; home in a bowl, 6; an old friend, 9.
Summer yellow-bird (Mnio-tiltidae), 47.
Sweet-pogonia (P. ophioglossoides), 145.
Swift, Jonathan, on parasites, 44.
Tennyson, quoted, 24.
"The Secrets of Nature in Forms and Fertilization of Flowers Discovered," Sprengel's work, 113.
Thevenot, concerning the thrift of insects, 152.
Tiger-beetle (Cicindela), 68.
Venus's-slipper (Cypripedium acaule), 205.
Vireo, abandons its nest, 45.
Wasps: —Wren, 10; microscopic, 45; tiny black, 69; digger, 72, 162; orange-spotted, 79; brown; mud, 161.
"Waxwork" bittersweet (Celastrus scandens), 88.
Welcome of the flowers: —The function of the stamen, 106; difference in cells, 107; condition of the flower, 108; physiological features; recognition of sex in flowers, 109; exchange of courtesies; each flower a law unto itself, 117; action of "jack-in-the-pulpit"; cypripedium and aristolochias; peculiarity of the sage, 119; queer stamens; nature's arrangement, 121; cross-fertilization insured, 122; showers of laurel pollen; curious construction of flower, 124; singular greeting to the bee, 126; remarkable interior arrangement of the Andromeda, 128; hidden anthers of the blue-flag, 129; intercommunication and reciprocity, 135.
Wild geranium (G. sylvaticum), 112.
Wild volapuek, 4.
Wilson, cow-bird's eggs, 33.
Wind as a fertilizing agent, 154.
White, Gilbert, cuckoo's eggs, 32; rich localities, 58.
Wood, Alphonso: —On tubercles, 203; on embarrassed bees, 235.
Wren-wasp (Odynerus flavipes): —A cumbersome prize, 10; selecting a home; way stations; a second instalment, 11; very familiar, 12; a well-stocked home, 13; impotent anaesthetic, 14; manner of catching her prey; a hypodermic injection, 15; food on storage; closing the cell after depositing egg, 16; living food; preference for ready-made houses; resemblance to the yellow-jacket, 17.
Zenarchus, concerning the cicada, 96.
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