148 Mr. C. Darwin on the FertiUzation of Orchids. 



disks do not stand far apart, have curious contrivances, such 

 as a channelled labellum, lateral shields, &c., compelling 

 moths to insert their proboscides directly in front. PL Hookerij 

 on the other hand {;ihicl. vol. xxxiv, 1862, p. 143), differs in a 

 very interesting manner : the two viscid disks stand widely 

 separated from each other; consequently a moth, unless of 

 gigantic size, would be able to suck the copious nectar without 

 touching either disk ; but this risk is avoided in the following 

 manner : — The central line of the stigma is prominent, and the 

 labellum, instead of hanging down, as in most of the other 

 species, is curved upwards, so that the front of the flower is 

 made somcAvhat tubular and is divided into two halves. Thus 

 a moth is compelled to go to one or the other side, and its 

 face will almost certainly be brought into contact with one of 

 the disks. The drum of the pollinium, when removed, con- 

 tracts in the same manner as I have described under PI. chlo- 

 rantha. Prof. Gray has seen a butterfly from Canada with 

 the pollinia of this species attached to each eye. In the case 

 of Platanthera fiava (American Journal of Science, vol. xxxvi. 

 1863, p. 292), moths are compelled in a different manner to 

 enter the nectary on one side. A narrow but strong protube- 

 rance, rising from the base of the labellum, projects upwards 

 and backwards, so as almost to touch the column ; thus the 

 moth, being forced to go to either side, is almost sure to 

 withdraw one of the viscid disks. In the allied and wonderful 

 Bonatea sjjeciosa of the Cape of Good Hope there is a similar 

 contrivance for the same purpose. 



Platanthera hyperhorea and dtlatata have been regarded 

 by some botanists as varieties of the same species ; and Prof. 

 Asa Gray says (Amer. Journ. of Science, vol. xxxiv. 1862, 

 pp. 259 & 425) that he has often been tempted to come to the 

 same conclusion ; but now, on closer examination, he finds, 

 besides other characters, a remarkable physiological difference, 

 namely, that PL dilatata^ like its congeners, requires insect aid 

 and cannot fertilize itself ; whilst in PL hyperhorea the pollen- 

 masses commonly fall out of the anther-cells whilst the flower 

 is very young or in bud, and thus the stigma is self-fertilized. 

 Nevertheless the various structures adapted for crossing are 

 still present. 



FertiUzation of Epipactis palustris (p. 102). — My son, Mr. 

 W. E.Darwin, has carefully observed for me this plant in the 

 Isle of Wight. Hive-bees seem to be the chief agents in fer- 

 tilization ; for he saw about a score of flowers visited by these 

 insects, many of which had pollen-masses attached to their 

 foreheads, just above the mandibles. I had supposed that in- 

 sects crawled into the flowers ; but hivc-bccs arc too large to 



