Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/134

114 after the other. I believe humble-bees generally act in this manner when visiting a dense spike of flowers, as it is the most convenient method; on the same principle that a woodpecker always climbs up a tree in search of insects. This seems an insignificant observation; but see the result. In the early morning, when the bee starts on her rounds, let us suppose that she alighted on the summit of a spike; she would certainly extract the pollinia from the uppermost and last opened flowers; but when visiting the next succeeding flower, of which the column in all probability would not as yet have moved from the labellum (for this is slowly and very gradually effected), the pollen-masses would be brushed off her proboscis and wasted. But nature suffers no such waste. The bee goes first to the lowest flower, and, crawling spirally up the spike, effects nothing on the first spike which she visits till she reaches the upper flowers, and then she withdraws the pollinia. She soon flies to another plant, and, alighting on the lowest and oldest flower, into which a wide passage will have been formed from the greater reflexion of the column, the pollinia strike the protuberant stigma. If the stigma of the lowest flower has already been fully fertilised, little or no pollen will be left on its dried surface; but on the next succeeding flower, of which the stigma is adhesive, large sheets of pollen will be left. Then as soon as the bee arrives near the summit of the spike she will withdraw fresh pollinia, will fly to the lower flowers on another plant, and fertilise them; and thus, as she goes her rounds and adds to her store of honey, she continually fertilises fresh flowers and perpetuates the race of our autumnal Spiranthes, which will yield honey to future generations of bees.

Spiranthes australis.—This species, an inhabitant