Part 5 (1/2)

I had never chanced to read of this flower in the literature of cross-fertilization, and murmuring, half aloud, ”What pretty mystery is yours, my Collinsonia?” prepared to investigate.

[Ill.u.s.tration: Fig. 9]

What I observed is pictured severally at Fig. 9, the flowers being shown from above, showing the two spreading stamens and the decidedly exceptional unsymmetrical position of the long style extending to the side. A small nectar-seeking b.u.mblebee had approached, and in alighting upon the fringed platform grasped the filaments for support, and thus clapped the pollen against his sides. Reasoning from a.n.a.logy, it would of course be absolutely clear that this pollen has thus been deposited where it will come in contact with the stigma of another flower. So, of course, it proved. In the bee's continual visits to the several flowers he came at length to the younger blooms, where the forked stigmas were turned directly to the front, while the immature stamens were still curled up in the flower tubes. Even the unopened buds showed a number of species where the early matured stigma actually protruded through a tiny orifice in precisely the right position to strike the pollen-dusted body of the bee, as he forced his tongue through the tiny aperture.[A]

[Footnote A: In numerous instances observed since the above was written I have noted the larger b.u.mblebees upon the blossom. These insects have a different method of approach, hanging beneath the flower, the anthers being clapped against their thorax at the juncture of the wings, instead of the abdomen, as in the smaller bee.]

[Ill.u.s.tration]

If their dainty mechanism excite our wonder, what shall be said of the revelations in the great order of the Compositae, where each so-called flower, as in the dandelion, daisy, cone-flower, marigold, is really a dense cl.u.s.ter of minute flowers, each as perfect in its construction as in the examples already mentioned, each with its own peculiar plan designed to insure the transfer of its own pollen to the stigma of its neighbor, while excluding it from its own?

All summer long the cone-flower, Fig. 10 (_Rudbeckia hirta_), blooms in our fields, but how few of us imagine the strange processes which are being enacted in that purple cone! Let us examine it closely. If we pluck one of the blossom's heads and keep it in a vase over-night, we shall probably see on the following morning a tiny yellow ring of pollen encircling the outer edge of the cone. In this way only are we likely to see the ring in its perfection, as in a state of nature the wind and insects rarely permit it to remain.

[Ill.u.s.tration: Fig. 10]

If we now with a sharp knife make a vertical section, as shown at A (Fig. 3), we may observe the conical receptacle studded with its embryo seeds, each bearing a tiny tubular blossom. Three distinct forms of these flowers are to be seen. The lower and older ones are conspicuous by their double feathery tails, the next by their extended anthers bearing the pollen at their extremity, and above these again the buds in all stages of growth. These various states are indicated in Fig. 11.

As in all the Compositae, the anthers are here united in a tube, the pollen being discharged within. At the base of this anther-tube rises the pistil, which gradually elongates, and like a piston forces out the pollen at the top. Small insects in creeping over the cone quickly dislodge it. In the next stage the anthers have withered, the flower-tube elongated, and the top of the two-parted pistil begins to protrude, and at length expands its tips, disclosing at the centre the stigmatic surface, which has until now been protected by close contact.

(See section.)

[Ill.u.s.tration: Fig. 11]

A glance at Fig. 11 will reveal the plan involved. The ring of pollen is inevitably scattered to the stigmas of the neighboring flowers, and cross-fertilization continually insured. Similar contrivances are to be found in most of the Compositae, through the same method being variously applied.

Perhaps even more remarkable than any of the foregoing, which are more or less automatic in their movements, is the truly astonis.h.i.+ng and seemingly conscious mechanism displayed in the wild arum of Great Britain--the ”lords and ladies” of the village lanes, the foreign counterpart of our well-known jack-in-the-pulpit, or Indian-turnip, with its purple-streaked canopy, and sleek ”preacher” standing erect beneath it. A representation of this arum is shown in Fig. 12, and a cross section at A, properly indexed.

[Ill.u.s.tration: Fig. 12]

How confidently would the superficial--nay, even careful--examination of one of the old-time botanists have interpreted its structure: ”How simple and perfect the structure! Observe how the anthers are placed so that pollen shall naturally fall directly on the stigmas and fertilize them!” Such would indeed appear to be intended, until it is actually discovered that the _stigmas have withered_ when the pollen is shed--a device which, acting in a.s.sociation with the little ring of hairs, tells a strange story. It is not my fortune to have seen one of these singular blossoms, but from the description of the process of fertilization given in Hermann Muller's wonderful work, aided by a botanical ill.u.s.tration of the structure of the flower, I am readily enabled to picture the progressive stages of the mechanism.

[Ill.u.s.tration: Fig. 13]

In the first stage (B, Fig. 13) small flies with bodies dusted with pollen from a previous arum blossom (for insects, as a rule, remain faithful or partial to one species of flowers while it is in bloom) are entering the narrowed tube, easily pa.s.sing through the drooping fringe of hairs. Nectar is secreted by the stigmas, and here the flies a.s.semble, thus dusting them with pollen. Their appet.i.te temporarily satisfied, the insects seek escape, but find their exit effectually barred by the intruding fringe of hairs (C). In this second stage the stigmas, having now been fertilized, have withered, at the same time exuding a fresh supply of nectar, which again attracts the flies, whereupon, as shown at D, the anthers open and discharge their pollen upon the insects. In the fourth stage (E), all the functions of the flower having now been fulfilled, the fringe of hairs withers, and the imprisoned pollen-laden flies are permitted to escape to another flower, where the beautiful scheme is again enacted.

In a paper of this kind it is of course possible only to hint at a few representative examples of floral mechanisms, but these would be indeed incomplete without a closing reference to that wonderful tribe of flowers with which the theory of cross-fertilization will ever be memorably a.s.sociated. I have previously alluded to the absolute dependence of the red clover upon the b.u.mblebee. This instance may be considered somewhat exceptional, though numerous parallel cases are known. Among ordinary flowers this intervention of the insect is largely a _preferable_ intention, and though almost invariably fulfilled, a large proportion of flowers still retain, as a _dernier ressort_, the power of at least partial self-fertilization and perpetuity in the absence or neglect of their insect counterpart.

[Ill.u.s.tration: Fig. 14]

The numerous and conclusive demonstrations of Darwin, however, have proved that in the compet.i.tion for existence such self-fertilized offspring quickly yield before the progeny of cross-fertilization.

But the distinctive feature of the orchids lies in the fact that this dependence on the insect is wellnigh universally absolute. Here are a great host of plants which are doomed to extinction if for any reason their insect sponsors should permanently neglect them. The princ.i.p.al botanical feature which differentiates the orchid from other plants lies in the construction of the floral organs, the pistil, stigma, and anthers here being united into a distinct part known as the column. The pollen is, moreover, peculiar, being collected into more or less compact ma.s.ses, and variously concealed in the flower. Some of these are club-shaped, with a viscid extremity, others of the consistency of a sticking-plaster, and all are hidden from external view in pouches and pockets, from which they never emerge unless withdrawn on the body of an insect. The various devices by which this removal is insured are most astonis.h.i.+ng and awe-inspiring. Nor is it necessary to go to the conservatory for a tropical specimen, as is commonly supposed. An orchid is an orchid wherever it grows, and our native list of some fifty species will afford examples of as strange mechanical adaptations as are to be found among Darwin's pages. Indeed, a few of our American species are there described. One example will suffice for present ill.u.s.tration--the sweet-pogonia or gra.s.s-pink of our sedgy swamps (_Pogonia ophioglossoides_). Its solitary rosy blossom, nodding on its slender stem above the sedges, is always a welcome episode to the sauntering botanist, and its perfume, suggesting ripe red raspberries, is unique in the wild bouquet. One of these flowers is shown in profile at Fig. 14, its various parts indexed. Concealed behind the petals is the column, elsewhere indicated from various points of view. Attracted by its color and fragrance, the insect seeks the flower; its outstretched fringy lip offers a cordial invitation at its threshold, and conducts its visitor directly to the sweets above. In his entrance, as seen at D (Fig. 15), the narrowed pa.s.sage compresses his back against the underside of the column, forcing his head and back against the stigma. The effect of this inward pressure, as will be seen, only serves to force the anther more firmly within its pocket; but as the insect, having drained the nectar, now backs out, note the result. The lip of the anther catches upon the back, swings outward on its hinge, and deposits its sticky pollen all over the insect's back, returning to its original position after his departure. In another moment he is seen upon another blossom, as at D again, his pollen-laden back now coming in contact with the stigma, and the intention of the blossom is accomplished; for without this a.s.sistance from the insect the little lid remains close within its pocket, and the pollen is thus retained.

[Ill.u.s.tration: Fig. 15]

What startling disclosures are revealed to the inward eye within the hearts of all these strange orchidaceous flowers! Blossoms whose functions, through long eras of adaptation, have gradually shaped themselves to the forms of certain chosen insect sponsors; blossoms whose chalices are literally fas.h.i.+oned to bees or b.u.t.terflies; blossoms whose slender, prolonged nectaries invite and reward the murmuring sphinx-moth alone, the floral throat closely embracing his head while it attaches its pollen ma.s.ses to the bulging eyes, or perchance to the capillary tongue! And thus in endless modifications, evidences all of the same deep vital purpose.

Let us then content ourselves no longer with being mere ”botanists”--historians of structural facts. The flowers are not mere comely or curious vegetable creations, with colors, odors, petals, stamens, and innumerable technical attributes. The wonted insight alike of scientist, philosopher, theologian, and dreamer is now repudiated in the new revelation. Beauty is not ”its own excuse for being,” nor was fragrance ever ”wasted on the desert air.” The seer has at last heard and interpreted the voice in the wilderness. The flower is no longer a simple pa.s.sive victim in the busy bee's sweet pillage, but rather a conscious being, with hopes, aspirations, and companions.h.i.+ps. The insect is its counterpart. Its fragrance is but a perfumed whisper of welcome, its color is as the wooing blush and rosy lip, its portals are decked for his coming, and its sweet hospitalities humored to his tarrying; and as it finally speeds its parting affinity rests content that its life's consummation has been fulfilled.

_A HONEY-DEW PICNIC_

[Ill.u.s.tration]