Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/222

202 no fissure along their lower surfaces for the protrusion of the caudicles. The exterior pollen-grains are square and have thicker walls than the interior grains, just as in the proper male pollen; and, what is very curious, each cell has its nucleus. Now, E. Brown states that in the early stages of the formation of the pollen-grains of ordinary Orchids (as with other plants) a minute nucleus is often visible; so that the rudimentary pollen-grains of Monachanthus apparently have retained—as is so general with rudiments in the animal kingdom—an embryonic character. Lastly, at the base, within each flask-shaped pollen-mass, there is a little mass of brown elastic tissue,—that is, a vestige of a caudicle,—which runs far up the pointed end of the flask, but does not (at least in some of the specimens) come to the surface, and could never be attached to any part of the pedicel. These rudimentary and enclosed caudicles are, therefore, utterly useless. Notwithstanding the small size and almost aborted condition of the female pollen-masses, when they were placed by Dr. Crüger within the stigma of a female plant they emitted "here and there a rudimentary tube." The petals then faded and the ovarium enlarged, but after a week it turned yellow and finally dropped off without bringing any seeds to perfection. This appears to me a very curious instance of the slow and gradual manner in which structures are modified; for the female pollen-masses, which can never be naturally removed or applied to the stigma, still partially retain their former powers and function.

Thus every detail of structure which characterises the male pollen-masses is represented in the female plant in a useless condition. Such cases are familiar to