146 Mr. C. Darwin oyi the Fertilization of Orchids. 



of the labellum stands so close to the anther and stigma, that 

 insects always enter the flower at one corner, between the 

 margin of the labelhim and one of the upper petals ; they also 

 ahiiost always crawl in with their backs turned directly or 

 obliquely towards the labellum. My son saw several which 

 had begun to crawl into the flower in a diflerent position ; but 

 they came out and changed their position. Thus, standing in 

 either corner of the flower, with their backs turned towards 

 the labellum, they inserted their heads and fore legs into the 

 short nectary, which is seated between the two widely sepa- 

 rated viscid disks. I ascertained that they stand in this po- 

 sition by finding three dead insects, which had been per- 

 manently glued to the disks. Whilst sucking the nectar, 

 which occupies about two or three minutes, the projecting 

 joint of the femur stands under the large helmet-like viscid 

 disk on either side ; and when the insect retreats, the disk 

 exactly fits on, and is glued to, the prominent joint. The 

 movement of depression in the caudicle then takes place, and 

 the mass of pollen-grains projects just beyond the tibia; so 

 that the insect, when entering another flower, can hardly fail 

 to fertilize the stigma, which is situated directly beneath the 

 disk on either side. I know of hardly any other case in 

 which the whole structure of the flower is more beautifully 

 correlated than in the Herminiuvi for a most peculiar manner 

 of fertilization. 



On the movement of tlie polUnia in Peristylus viridis (p. 76). 

 — Mr. T. H. Farrer informs me that the pollinia certainly un- 

 dergo a movement of depression, but that this does not take 

 place until twenty or thirty minutes have elapsed after their 

 removal from the anther-cases. This length of time probably 

 accounls for my oversight. He asserts that, after the move- 

 ment of depression, the pollinia become much better adapted 

 to strike the stigmatic surface. He suggests that insects may 

 take a long time to lick up the nectar from the two naked 

 spots on the labellum, and through the narrow sHt-like open- 

 ing into the nectary — and that during this time the polli- 

 nium becomes firmly attached, by the slow hardening of the 

 viscid matter, to the insect's body, so as to be subsequently 

 ready to fertilize another flower when visited by the same 

 insect. 



On the Lepido^Jtera which fertilize the Gymnadenia conopsea, 

 and on the divergence of the pollinia (p. 82). — Mr. George 

 Darwin went at night to a bank where this species grows 

 plentifully, and soon caught Plusia chrysitis with six polHnia, 

 P. gamma with three, Anaitis plagiata with five, and Tri- 

 j)h(ena pronuhawiih seven pollinia attached to their proboscides. 



