Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/282

262 the caudicle is actually more than thrice as long as the elongated pollen-masses; and it is highly improbable that so lengthy a mass of grains, slightly cohering together by the aid of elastic threads, should ever have existed, as an insect could not have safely transported and applied a mass of this shape and size to the stigma of another flower.

We have hitherto considered gradations in the state of the same organ. To any one with more knowledge than I possess, it would be an interesting subject to trace the gradations between the several species and groups of species in this great and closely-connected order. But to make a perfect gradation, all the extinct forms which have ever existed, along many lines of descent converging to the common progenitor of the group, would have to be called back into life. It is due to their absence, and to the consequent wide gaps in the series, that we are enabled to divide the existing species into definable groups, such as genera, families, and tribes. If there had been no extinction, there would still have been great lines or branches of special development,—the Vandeæ, for instance, would still have been distinguishable as a great body, from the great body of the Ophreæ; but ancient and intermediate forms, very different probably from their present descendants, would have rendered it utterly impossible to separate by distinct characters the one great body from the other.

I will venture on only a few more remarks. Cypripedium, in having three stigmas developed, and therefore in not possessing a rostellum, in having two fertile anthers with a large rudiment of a third, and in the state of its pollen, seems a remnant of the order whilst in a simpler or more generalised condition. Apostasia