204 ORIGIN OF SPECIES 



which stand above it; and when the bucket is half full, the 

 water overflows by a spout on one side. The basal part of 

 the labellum stands over the bucket, and is itself hollowed 

 out into a sort of chamber with two lateral entrances ; with- 

 in this chamber there are curious fleshy ridges. The most 

 ingenious man, if he had not witnessed what takes place, 

 could never have imagined what purpose all these parts serve. 

 But Dr. Criiger saw crowds of large humble-bees visiting the 

 gigantic flowers of this orchid, not in order to suck nectar, 

 but to gnaw off the ridges within the chamber above the 

 bucket ; in doing this they frequently pushed each other into 

 the bucket, and their wings being thus wetted they could not 

 fly away, but were compelled to crawl out through the pas- 

 sage formed by the spout or overflow. Dr. Criiger saw a 

 "continual procession" of bees thus crawling out of their 

 involuntary bath. The passage is narrow, and is roofed over 

 by the column, so that a bee, in forcing its way out, first rubs 

 its back against the viscid stigma and then against the viscid 

 glands of the pollen-masses. The pollen-masses are thus 

 glued to the back of the bee which first happens to crawl out 

 through the passage of a lately expanded flower, and are 

 thus carried away. Dr. Criiger sent me a flower in spirits of 

 wine, with a bee which he had killed before it had quite 

 crawled out with a pollen-mass still fastened to its back. 

 When the bee, thus provided, flies to another flower, or to 

 the same flower a second time, and is pushed by its comrades 

 into the bucket and then crawls out by the passage, the 

 pollen-mass necessarily comes first into contact with the 

 viscid stigma, and adheres to it, and the flower is fertilised. 

 Now at last we see the full use of every part of the flower, 

 of the water-secreting horns, of the bucket half full of water, 

 "ivhich prevents the bees from flying away, and forces them 

 to crawl out through the spout, and rub against the properly 

 placed viscid pollen-masses and the viscid stigma. 



The construction of the flower in another closely allied 

 orchid, namely the Catasetum, is widely different, though 

 serving the same end; and is equally curious. Bees visit 

 these flowers, like those of the Coryanthes, in order to gnaw 

 the labellum; in doing this they inevitably touch a long, 

 tapering, sensitive projection, or, as I have called it, the 



