Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/133

. IV. younger flowers. Nevertheless, a flower which in its early state had not been visited by insects would not necessarily, in its later and more expanded condition, have its pollen wasted; for insects, in inserting and withdrawing their proboscides, bow them forwards or upwards, and would thus often strike the furrow in the rostellum. I imitated this action with a bristle, and often succeeded in withdrawing the pollinia from old flowers. I was led to make this trial from having at first chosen old flowers for examination; and on passing a bristle, or fine culm of grass, straight down into the nectary, the pollinia were never withdrawn; but when it was bowed forward, I succeeded. Flowers which have not had their pollinia removed can be fertilised as easily as those which have lost them; and I have seen not a few cases of flowers with their pollinia still in place, with sheets of pollen on their stigmas.

At Torquay I watched for about half an hour a number of these flowers growing together, and saw three humble-bees of two kinds visit them. I caught one and examined its proboscis: on the superior lamina, some little way from the tip, two perfect pollinia were attached, and three other boat-formed discs without pollen; so that this bee had removed the pollinia from five flowers, and had probably left the pollen of three on the stigmas of other flowers. The next day I watched the same flowers for a quarter of an hour, and caught another humble-bee at work; one perfect pollinium and four boat-formed discs adhered to its proboscis, one on the top of the other, showing how exactly the same part of the rostellum had each time been touched.

The bees always alighted at the bottom of the spike, and, crawling spirally up it, sucked one flower