Mr. C Darwin on the Fertilization of Orchids. 



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

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

 moths to insert their proLoscides directly in front. PI. Ifookerij 

 on the other hand {ibid. vol. xxxiv. 18C2, 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 liower is 

 made somewhat 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 certaiidy be brought into contact witli one of 

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

 tracts in the same maimer as I have described under PL chlo- 

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

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

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

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

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

 rance, risuig 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 s]>eciosu of the Cape of Good Hope there is a similar 

 contrivance for the same.pur])ose. 



Platanthera hi/jyerhorea and dilatata 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 hyperlorea 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. 



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

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

 Isle of Wight. I live-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 su))posed that in- 

 sects crawled into the flowers ; but hive-bees are too large to 



