Mr. C. Darwin on the Fertilization of Orchids. 1 7 



beset with minute, rigid, sliarp-pointed papilla, all directed 

 forwards, which are excellently adapted to brush off the pollen 

 from an insect's head or back." 



The u.ie of the copious fluid contained within the Jahellum 

 o/Coryanthes (p. 278). — The Goryanthes macrantha is per- 

 haps tlie most wonderful of all known orcliids, even more 

 wonderful in structure and function than Catasetum. Its 

 manner of fej-tilization has been described bj Dr. Criiger in 

 the 'Journal of the Linnean Society' (vol. viii. Bot. 1864, 

 p. 130) , and in letters to me. He sent me bees, belonging to 

 the genus Eiiglossa, which he saw at work. The fluid in the 

 bucket formed by the basal part of the labellum is not nectar 

 and does not attract insects, but serves, by wetting their 

 wings, to prevent them from crawling out except through the 

 small passages close to the anther and stigma. Thus the 

 secretion of fluid in this orchis serves exactly the same end as 

 the inflected margins of the labellum in Cypripedium. 



On the evidence that Insects visit many exotic Orchids in order 

 to gnato parts of the labellum., and not for the sake of nectar 

 (p. 284). — It has been highly satisfactory to me that this hypo- 

 thesis has been fully confirmed. In the West Indies, Dr. Criiger 

 witnessed humble-bees of the genus Euglossa gnawing the 

 labellum of Catasetum, Goryanthes, Gongora, and Stanhopea ; 

 and Fritz Miiller has repeatedly found, in South Brazil, the 

 prominences on the labellum of Oncidium gnawed. We are 

 thus enabled to understand the meaning of the various extra- 

 ordinary crests and projections on the labellum of various 

 exotic orchids ; for they invariably stand in such a position 

 that insects, whilst gnawing them, will be almost sure to 

 touch the viscid disks of the pollinia, and thus remove them. 



Bonatea speciosa (p. 30.5). — T!ie manner oi fertilization oi 

 this extraordinary orchis has now been frdly described by Mr. 

 E. Trimen in the 'Journal of the Linnean Society' (vol. ix. 

 Bot. 1865, p. 156). A projection rising from the base of the 

 labellum is one of its most remarkable peculiarities, as an in- 

 sect is thus compelled to insert its proboscis on one side, and 

 thus to touch one of the two widely separated and projecting 

 viscid disks. Mr. J. P. Mansel Weale has also published 

 [ibid. vol. X. 1869, p. 470) analogous observations on a second 

 species, viz. Bonatea Darwinii. Mr. Weale caught a skipper- 

 butterfly {Pyrgus ehno) quite embarrassed by the number of 

 pollinia belonging to this orchis which adhered to its sternum. 

 I do not know of any other case in which the pollinia adhere 

 to the sternum of a Lepidopterous insect. 



On the nature of the contraction which causes the pollinia, 

 after their removal from the anther, to change their position 



B 



