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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.
Accepting it as a postulate that every detail of the apparatus must be equally essential for the purpose it had to serve, he made a series of experiments which demonstrated that some insect of Madagascar doubtless a moth must be equipped with a proboscis long enough to reach the nectar, and at the same time thick enough at the base to withdraw the pollinia thus fertilizing the bloom.
For, if the nectar had lain so close to the orifice that moths with a proboscis of reasonable length and thickness could get at it, they would drain the cup without touching the pollinia. Darwin never proved his special genius more admirably than in this case.
This is all that you will find to represent the stamens of the flower. When these masses of pollen, or pollinia as they are called, are within the flower, the knob at the bottom is covered by a little lid, shutting them in like the lid of a box, and just below this lid you will see two yellowish lumps, which are very sticky.
See the marvellous fashion in which the Orchis Moris, our humble country orchid, combines the play of its rostellum and retinacula; observe the mathematical and automatic inclination and adhesion of its pollinia; as also the unerring double seesaw of the anthers of the wild sage, which touch the body of the visiting insect at a particular spot in order that the insect may, in its turn, touch the stigma of the neighbouring flower at another particular spot; watch, too, in the case of the Pedicularis Sylvatica, the successive, calculated movements of its stigma; and indeed the entrance of the bee into any one of these three flowers sets every organ vibrating, just as the skilful marksman who hits the black spot on the target will cause all the figures to move in the elaborate mechanisms we see in our village fairs.
As I have fully treated this subject in another work, I will here give only a few details on one alone of the most striking peculiarities of the flowers of orchids, namely, their pollinia. A pollinium, when highly developed, consists of a mass of pollen-grains, affixed to an elastic foot-stalk or caudicle, and this to a little mass of extremely viscid matter.
But if the bee went into the next flower with these pollinia sticking upright, she would simply put them into the same slits in the next flower, she would not touch them against the stigma. Nature, however, has provided against this.
The pollinia are by this means transported by insects from one flower to the stigma of another.
With the pollinia of orchids, the threads which originally served to tie together the pollen-grains, can be traced cohering into caudicles; and the steps can likewise be followed by which viscid matter, such as that secreted by the stigmas of ordinary flowers, and still subserving nearly but not quite the same purpose, became attached to the free ends of the caudicles all these gradations being of manifest benefit to the plants in question.
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