Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/186

166 nectary had been acquired by successive modifications. As certain moths of Madagascar became larger through natural selection in relation to their general conditions of life, either in the larval or mature state, or as the proboscis alone was lengthened to obtain honey from the Angræcum and other deep tubular flowers, those individual plants of the Angræcum which had the longest nectaries (and the nectary varies much in length in some Orchids), and which, consequently, compelled the moths to insert their proboscides up to the very base, would be best fertilised. These plants would yield most seed, and the seedlings would generally inherit long nectaries; and so it would be in successive generations of the plant and of the moth. Thus it would appear that there has been a race in gaining length between the nectary of the Angræcum and the proboscis of certain moths; but the Angræcum has triumphed, for it flourishes and abounds in the forests of Madagascar, and still troubles each moth to insert its proboscis as deeply as possible in order to drain the last drop of nectar.

I could add descriptions of many other curious structures in the Vandeæ, more especially from the letters of Fritz Müller with respect to those of Brazil; but the reader would be wearied. I must, however, make a few remarks on certain genera, the fertilisation of which remains a mystery, chiefly on account of the narrowness of the mouth of the stigma, as this renders the insertion of the pollen-masses extremely difficult. Two closely allied species or varieties of Acropera, viz., A. luteola and loddigesii have been observed by me during several seasons, and every detail of their structure seems as if specially adapted to render their fertilisation almost impossible. I have met with hardly