Page:On the Various Contrivances by Which British and Foreign Orchids are Fertilised by Insects, and on the Good Effects of Intercrossing.djvu/92

 whatever their nature may be, which will bring all the parts into more perfect harmony with each other, will be seized on and preserved by natural selection.

To give a simple illustration: in many Orchids the ovarium (but sometimes the footstalk) becomes for a period twisted, causing the labellum to hang downwards, so that insects can easily visit the flower; but from slow changes in the form and position of the petals, or from new sorts of insects visiting the flower, it might become advantageous to the plant that the labellum should resume its normal upward position, as is actually the case with Malaxis paludosa; this change, it is obvious, might be simply effected by the continued selection of varieties which had their ovarium a little less twisted; but if the plant only afforded varieties with the ovarium more twisted, the same end could be attained by their selection until the flower had turned completely round on its axis: this seems to have occurred with the Malaxis, for the labellum has acquired its present upward position, and the ovarium is twisted to excess.

Again, we have seen that in most Vandee there is a plain relation between the depth of the stigmatic chamber and the length of the pedicel, by which the pollen-masses are inserted; now if the chamber became slightly less deep from any change in the form of the column or any other unknown cause, the shortening of the pedicel would be the simplest corresponding change; but if the pedicel did not happen to vary in lenth, and the slightest tendency to an upward curvature from elasticity as in Phalenopsis, or to a backward hygrometric movement as in one of the Maxillarias, would be preserved, and the tendency would be continually augmented by selection; thus the pedicel, as far as its action is concerned, would be modified in the same manner as if it had been shortened. Such processes carried on during many thousand generations in various ways, with the several parts of the flower, would create an endless diversity of coadapted structures for the same general purpose. This view affords, I believe, the key which partly solves the problem of the vast diversity of structure adapted for closely analogous ends in many large groups of organic beings.

The more I study nature, the more I become impressed with ever-increasing force with the conclusion, that the contrivances and beautiful adaptations slowly acquired through each part occasionally varying in a slight degree in many ways, with the preservation or natural selection of those variations which are beneficial to the organism under the complex and ever-varying conditions of life, transcend in an incomparable degree the contrivances and adaptations which the most fertile imagination of the most imaginative man could suggest with unlimited time at his disposal. The use of each trifling detail of structure is far from a barren search to those who believe in natural selection. When a naturalist casually takes up an organic being, and does not study its whole life (imperfect though that study will ever be), he naturally doubts whether each trifling point can be of any use, or indeed whether it be due to any general law. Some naturalists believe that numberless structures have been created for the sake of mere variety and beauty, much as a workman would make a set of different patterns. I, for one, have often and often doubted whether this or that detail of structure could be of any service; yet, if of no good, these structures could not have been modelled by the natural preservation of useful variations; such details could only be vagely accounted for by the direct action of the conditions of life, or the mysterious laws of correlation of growth.

To give nearly all the instances of trifling details of structure in the flowers of Orchids, which are certainly of high importance, would be to recapitulate a great portion of this volume. But I will recall to the reader's memory a few cases. I do not here refer to the fundamental framework of the plant, such as the remnants of the fifteen primary organs arranged alternately in the five worls; for nearly all those who believe in the modification of organic beings will admit that their presence is due to inheritance from a remote parent-form. A series of facts with respect to the use of the variously shaped and placed petals and sepals has just been enumerated. So, again, the importance of the slight differences in the shape of the caudicle of the pollinium of the Bee Ophrys, compared with that of the other species of the genus, has just been referred to: to this might be added the doubly-bent caudicle of the Fly Ophrys: indeed, the important relation of the length and shape of the caudicle, with reference to the position of the stigma, might be cited throughout whole tribes. The solid projecting knob of the anther in Epipactis palustris, which does not include pollen, when moved by insects, liberates the pollen-masses. In Cephalanthera grandiflora, the upright position of the flower, and its almost closed condition, protect from disturbance the slightly coherent pillars of pollen. The length and elasticity of the filament of the anther in certain species of Dendrobium apparently serves for self-fertilisation, if insects fail to transport the pollen-masses. The slight forward inclination of the crest of the rostellum in Listera prevents the anther-case being caught when the viscid matter explodes. The elasticity of the lip of the rostellum in Orchis causes it to spring up again when one pollen-mass is removed, thus keeping ready for action the second viscid disc, which otherwise would be wasted. The two nectar-secreting spots in the Frog Orchis, beneath the viscid discs at the base of the labellum, and the medial nectary in front of the stigma, are apparently necessary for the fertilisation of the flower. No one who had not studied Orchids