Chap. VI.] OF NATURAL SELECTION. 15ft 



lateral entrances; within 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 passage 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 s» 

 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, which 

 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 antenna. This antenna, when touched, transmits a 

 sensation or vibration to a certain membrane which is instantly 

 ruptured ; this sets free a spring by which the pollen-mass is shot 

 forth, like an arrow, in the right direction, and adheres by its 

 viscid extremity to the back of the bee. The pollen-mass of the 

 male plant (for the sexes are separate in this orchid) is thus carried 

 to the flower of the female plant, where it is brought into contact 

 with the stigma, which is viscid enough to break certain elastic 

 threads, and retaining the pollen, fertilisation is effected. 



How, it may be asked, in the foregoing and in ninumerable other 



