Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/175

. VI. very oddly shaped; and as the stigmatic chamber is deep and likewise curiously shaped, we are led to believe that the disc is fastened with great precision to the square projecting head of some insect.

In most eases there is a plain relation between the length of the pedicel and the depth of the stigmatic chamber, into which the pollen-masses have to be inserted. In some few cases, however, in which a long pedicel and a shallow stigma co-exist, we shall presently meet with curious compensating actions. After the disc and pedicel have been removed, the shape of the remaining part of the rostellum is of course altered, being now slightly shorter and thinner, and sometimes notched. In Stanhopea, the entire circumference of the extremity of the rostellum is removed, and a thin, pointed, needle-like process alone is left, which originally ran up the centre of the disc.

If we now turn to the diagram (fig. 23, p. 150), and suppose the rectangularly bent rostellum to be thinner and the stigma to lie closer beneath it than is there represented, we shall see that, if an insect with a pollinium attached to its head were to fly to another flower and occupy exactly the same position which it held whilst the attachment was effected, the pollen-masses would be in the right position for striking the stigma, especially if, from their weight, they were to become in the least degree depressed. This is all that takes place in Lycaste skinnerii, Cymbidiwm giganteum, Zygopetalum mackai, Angræcum eburneum, Miltonia clowesii, in a Warrea, and, I believe, in Galeandra funkii. But if in our diagram we suppose, for instance,