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



small viscid disks, and all the parts are so arranged that, if 

 insects were to visit the flowxrs, the pollen-masses Avould pro- 

 bably be removed and then carried to another flower, but not 

 so effectually as with most other orchids. We shall hereafter 

 find a few other cases of orchids which have structural pecu- 

 liarities adapted both for self-fertilization and for crossing. I 

 may here also refer to a paper by Mr. R. Trimen ( Journ. Linn. 

 8oc. vol. vii. Botany, 1863, p. 144) on the beautiful Disa 

 granclifiora of the Cape of Good Hope. This orchid presents 

 several remarkable characteristics, one of these being that the 

 pollinia do not spontaneously undergo any movement of de- 

 pression, the weight of the pollen-masses sufficing to bend the 

 caudicle into the proper curvature for the act of fertilization. 

 Another peculiarity is that the posterior sepal secretes nectar, 

 and is developed into a spur-like nectary. Mr. Trimen in- 

 forms me that he has seen a Dipterous insect, allied to Bom- 

 hylius, frequenting the flowers. I may add that Mr. Trimen 

 has sent me descriptions and specimens of various other South- 

 African orchids, which confirm the general conclusions at 

 Avhich I have arrived in my w^ork. 



On the movement of the pollinia o/Ophrys muscifera (p. 56). 

 — Mr. T. H. Farrer, who has lately been attending to the fer- 

 tilization of various plants, has convinced me that I have 

 erred, and that the pollinia of this Ophrys do undergo a move- 

 ment of depression. Hence my remarks on the correlation of 

 the various parts of the flower are to a certain extent invali- 

 dated ; but there can be no doubt that the naturally bent 

 caudicle plays an important part in placing the pollen-mass 

 in a proper position for striking the stigma. I have continued 

 occasionally to watch the flowers of this species, but have 

 never succeeded in seeing insects visit them ; but I have been 

 led to suspect that they puncture or gnaw the small lustrous 

 prominences beneath the viscid disks, which, I may add, are 

 likewise present in several allied species. I have observed 

 very minute punctures on these prominences, but I could not 

 decide whether these had been made by insects or whether 

 superficial cells had spontaneously burst. 



Ophrys aranifera (p. 63). — F. Delpino states (Fecondazione 

 nellePiante&c, Firenze, 1867, p. 19) that he has examined in 

 Italy thousands of specimens of this Op)hrys^ and that it sel- 

 dom produces capsules. It does not secrete any nectar. Al- 

 though he never saw an insect on the flowers (excepting once 

 a green locust), nevertheless they are fertilized by insects ; for 

 he found pollen on the stigmas of some flowers, which had their 

 own pollinia still within the anther-cases. The pollinia never 



