Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/73

stigma. The anther-cells naturally open soon after the flower is fully expanded, and the thick ends of the pollen-masses then fall out, the viscid discs still, remaining in their pouches. Slight as is the weight of the pollen-masses, yet the caudicles are so thin and quickly become so flexible, that in the course of a few hours they sink down, until they hang freely in the air

Fig. 8.

Ophrys apifera, or Bee Ophrys.

l. l.a. anther.

l. l. labellum.

A. Side view of flower, with the upper sepal and the two upper petals removed. One pollinium, with its disc still in its pouch, is represented as just falling out of the anther-cell; and the other has fallen almost to its full extent, opposite to the hidden stigmatic surface.

B. Pollinium in the position in which it lies embedded.

(see lower pollen-mass in fig. A) exactly opposite to and in front of the stigmatic surface. In this position a breath of air, acting on the expanded petals, sets the flexible and elastic caudicles vibrating, and they almost immediately strike the viscid stigma, and, being there secured, impregnation is effected. To make sure that no other aid was requisite, though