152 Mr. C. Darwin on the Fertilization of Orchids. 



the stigma ; so that everything here goes on as I have de- 

 scribed under Lister a ovata. The flowers are frequented by 

 minute Diptera and Hymenoptera. 



On the self-fertilization of Neottia nidus-avis, and on the 

 rostellum not exploding spontaneously (p. 153). — I covered up 

 with a net several plants, and after four days found that the 

 rostellum had not spontaneously exploded, and had already 

 almost lost this power. The pollen had become incoherent, 

 and in all the flowers much had fallen on the stigmatic sur- 

 faces, which were penetrated by pollen -tubes. The spreading 

 of the pollen seemed to be in part caused by the presence of 

 Thrij)s, many of which minute insects were crawling about 

 dusted all over with pollen. The covered-up plants produced 

 plenty of capsules, but these were much smaller and contained 

 much fewer seeds than the capsules produced by the adjoining 

 uncovered plants. I may here add that I detected on the crest 

 of the rostellum some minute rough points, which seemed 

 particularly/ sensitive in causing the rostellum to explode. 



Dr. H. Miiller, of Lippstadt, informs me that he has seen 

 Diptera sucking the nectar and removing the pollinia of this 

 plant. 



On the self-fertilization of certain Epidendrese (p. 166). — 

 Dr. Criiger says (Journ. Linn. Soc. vol. viii. Botany, 1864, 

 p. 131) that " we have in Trinidad three plants belonging to 

 the Epidendrese (a Bchomhurghia^ Gattleya^ and Epidendron) 

 which rarely open their flowers, and are invariably impreg- 

 nated when they do open them. In these cases it is easily 

 seen that the pollen-masses have been acted on by the stig- 

 matic fluid, and that the pollen-tubes descend from the pollen- 

 masses in situ down into the ovarian canal." Mr. Anderson, 

 a skilful cultivator of orchids in Scotland, informs me (see also 

 ' Cottage Gardener,' 1863, p. 206) that with him the flowers 

 of Dendrohium cretaceum never expand, and yet produce 

 capsules with plenty of seed, which, when examined by me, 

 was found to be perfectly good. These orchids make a near 

 approach to those dimorphic plants (as Oxalis, Ononis, and 

 Viola) which habitually produce open and perfect, as well as 

 closed and imperfect flowers. 



On the slow movement of the pollinia in Oncidium (p. 189). 

 — Mr. Charles Wright, in a letter to Prof. Asa Gray, states 

 that he observed in Cuba a pollinium of an Oncidium attached 

 to a Bomhus, and he concluded at first that I was completely 

 mistaken about the movement of depression ; but after several 

 hours the pollinium moved into the proper position for fertilizing 

 the flower. 



Manner of fertilization of various exotic Orchids (p. 189). 



