Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/155

. V. been carried away. Insects sometimes remove only one of the two pairs. I noticed a flower with all four pollen-leaves still in place, with a single one in the stigmatic cavity; and this must clearly have been brought by some insect. Within the stigmas of many other flowers pollen-leaves were observed. The plant produces plenty of seed; and thirteen of the twenty-one lower flowers on one spike had formed large capsules.

We will now turn to some exotic genera. The pollinia of Pleurothallis frolifera and ligulata (?) have a minute caudicle, and mechanical aid is requisite to force the viscid matter from the under side of the rostellum into the anther, thus to catch the caudicles and remove the pollinia. On the other hand, in our British Malaxis and in Microstylis rhedii from India, the upper surface of the minute tongue-shaped rostellum becomes viscid and adheres to the pollinia without any mechanical aid. This appears likewise to be the case with Stelis racemiflora, but the flowers were not in a good state for examination. I mention this latter flower partly because some insect in the hothouse at Kew had removed most of the pollinia, and had left some of them adhering to the lateral stigmas. These curious little flowers are widely expanded and much exposed; but after a time the three sepals close together with perfect exactness, so that it is scarcely possible to distinguish an old flower from a bud: yet, to my surprise, the closed flowers opened when immersed in water.

The allied Masdevallia fenestrata bears an extraordinary flower. The three sepals instead of closing, as in the case of Stelis after the flower has remained for a time expanded, cohere together and never open. Two minute, lateral, oval windows (hence the name fenestrata), are seated high up the flower opposite each