"Cross-fertilization," says Darwin, "results in offspring which vanquish the offspring of self-fertilization in the struggle for existence." This has been the motto of the orchid family for ages. No group of plants has taken more elaborate precautions against self-pollination or developed more elaborate and ingenious mechanism to compel insects to transfer their pollen than this.
The fissure down the front of the pink lady's slipper is not so wide but that a bee must use some force to push against its elastic sloping sides and enter the large banquet chamber where he finds generous entertainment secreted among the fine white hairs in the upper part. Presently he has feasted enough. Now one can hear him buzzing about inside, trying to find a way out of the trap. Toward the two little gleams of light through apertures at the end of a passage beyond the nectary hairs, he at length finds his way. Narrower and narrower grows the passage until it would seem as if he could never struggle through; nor can he until his back has rubbed along the sticky, overhanging stigma, which is furnished with minute, rigid, sharply pointed papillae, all directed forward, and placed there for the express purpose of combing out the pollen he has brought from another flower on his back or head. The imported pollen having been safely removed, he still has to struggle on toward freedom through one of the narrow openings, where an anther almost blocks his way.
As he works outward, this anther, drawn downward on its hinge, plasters his back with yellow granular pollen as a parting gift, and away he flies to another lady's slipper to have it combed out by the sticky stigma as described above. The smallest bees can squeeze through the passage without paying toll. To those of the Andrena and Halictus tribe the flower is evidently best adapted. Sometimes the largest bumblebees, either unable or unwilling to get out by the legitimate route, bite their way to liberty. Mutilated sacs are not uncommon. But when unable to get out by fair means, and too bewildered to escape by foul, the large bee must sometimes perish miserably in his gorgeous prison.
SHOWY, GAY, or SPRING ORCHIS
(Orchis spectabilis) Orchid family
Flowers - Purplish pink, of deeper and lighter shade, the lower lip white, and thick of texture; from 3 to 6 on a spike; fragrant. Sepals pointed, united, arching above the converging petals, and resembling a hood; lip large, spreading, prolonged into a spur, which is largest at the tip and as long as the twisted footstem. Sterm: 4 to 12 in. high, thick, fleshy, 5-sided. Leaves: 2 large, broadly ovate, glossy green, silvery on under side, rising from a few scales from root. Fruit: A sharply angled capsule, 1 in. long. Preferred Habitat - Rich, moist woods, especially under hemlocks. Flowering Season - April-June. Distribution - From New Brunswick and Ontario southward to our Southern States, westward to Nebraska.
Of the six floral leaves which every orchid, terrestrial or aerial, possesses, one is always peculiar in form, pouch-shaped, or a cornucopia filled with nectar, or a flaunted, fringed banner, or a broad platform for the insect visitors to alight on. Some orchids look to imaginative eyes as if they were masquerading in the disguise of bees, moths, frogs, birds, butterflies. A number of these queer freaks are to be found in Europe. Spring traps, adhesive plasters, and hair-triggers attached to explosive shells of pollen are among the many devices by which orchids compel insects to cross-fertilize them, these flowers as a family showing the most marvelous mechanism adapted to their requirements from insects in the whole floral kingdom. No other blossoms can so well afford to wear magenta, the ugliest shade nature produces, the "lovely rosy purple" of Dutch bulb growers, a color that has an unpleasant effect on not a few American stomachs outside of Hoboken.
But an orchid, from the amazing cleverness of its operations, is attractive under any circumstances to whomever understands it. This earliest member of the family to appear charms the female bumblebee, to whose anatomy it is especially adapted. The males, whose faces are hairy where the females' are bare, and therefore not calculated to retain the sticky pollen masses, are not yet flying when the showy orchis blooms. Bombus Americanorum, which can drain the longest spurs, B. separatus, B. terricola, and, rarely, butterflies as well, have been caught with its pollen masses attached. The bee alights on the projecting lip, pushes her head into the mouth of the corolla, and, as she sips the nectar from the horn of plenty, ruptures by the slight pressure a membrane of the pouch where two sticky buttons, to which two pollen masses are attached, lie imbedded. Instantly after contact these adhere to the round bare spots on her face, the viscid cement hardening before her head is fairly withdrawn. Now the diverging pollen masses, that look like antennae, fall from the perpendicular, by remarkable power of contraction, to a horizontal attitude, that they may be in the precise position to fertilize the stigma of the next flower visited - just as if they possessed a reasoning intelligence! Even after all the pollen has been deposited on the sticky stigmas of various blossoms, stump-like caudicles to which the two little sacs were attached have been found still plastered on a long-suffering bee. But so rich in nectar are the moisture-loving orchids that, to obtain a draught, the sticky plasters which she must carry do not seem too dear a price to pay. In this showy orchis the nectar often rises an eighth of an inch in the tube, and sufficient pressure to cause a rupture will eject it a foot.
ROSE or SWEET POGONIA; SNAKE-MOUTH
(Pogonia ophioglossoides) Orchid family
Flowers - Pale rose pink, fragrant, about 1 in. long, usually solitary at end of stem 8 to 15 in. high, and subtended by a leaf-like bract. Sepals and petals equal, oval, about 1/2 in. long, the lip spoon-shaped, crested, and fringed. Column shorter than petals, thick, club-shaped. Anther terminal, attached to back of column, pollen mass in each of its 2 sacs. Stigma a flattened disk below anther. Leaves: 1 to 3, erect, lance-oblong, sometimes one with long footstem from fibrous root. Preferred Habitat - Swamps and low meadows. Flowering Season - June-July. Distribution - Canada to Florida, westward to Kansas.
Rearing its head above the low sedges, often brightened with colonies of the grass pink at the same time, this shy recluse of the swamps woos the passing bee with lovely color, a fragrance like fresh red raspberries, an alluring alighting place all fringed and crested, and with the prospect of hospitable entertainment in the nectary beyond. So in she goes, between the platform and the column overhead, pushing first her head, then brushing her back against the stigma just below the end of the thick column that almost closes the passage. Any powdery pollen she brought on her back from another pogonia must now be brushed off against the sticky stigma. Her feast ended, out she backs. And now a wonderful thing happens. The lid of the anther which is at the end of the column, catching in her shoulders, swings outward on its elastic hinge, releasing a little shower of golden dust, which she must carry on the hairs of her head or back until the sticky stigma of the next pogonia entered kindly wipes it off! This is one of the few orchids whose pollen, usually found in masses, is not united by threads. Without the bee's aid in releasing it from its little box, the lovely species would quickly perish from the face of the earth.