282 CONCLUDING EEMAKKS. Chap. IX. 



highly attractive to the proper insects having increased 

 in number. We know that certain Orchids require 

 certain insects for their fertilisation, as in the cases be- 

 fore given of Vanilla and Sarcochilus. In Madagascar 

 Angrsecum sesquipedale must depend on some gigantic 

 moth. In Europe Cypripedium calceolus appears to be 

 fertilised only by small bees of the genus Andrena, 

 and Epipaetis latifolia only by wasps. In those cases 

 in which only a few flowers are impregnated owing, to 

 the proper insects visiting only a few, this may be a 

 great injury to the plant ; and many hundred species 

 throughout the world have been thus exterminated ; 

 those which survive having been favoured in some 

 other way. On the other hand, the few seeds which 

 are produced in these cases will be the product of 

 cross-fertilisation, and this as we now positively know 

 is an immense advantage to most plants. 



I have how nearly finished this volume, which is 

 perhaps too lengthy. It has, I think, been shown that 

 the Orchidese exhibit an almost endless diversity of 

 beautiful adaptations. When this or that part has been 

 spoken of as adapted for some special purpose, it must 

 not be supposed that it was originally always formed 

 for this sole purpose. The regular course of events 

 seems to be, that a part which originally served for one 

 purpose, becomes adapted by slow changes for widely 

 different purposes. To give an instance: in all the 

 Ophreae, the long and nearly rigid caudicle manifestly 

 serves for the application of the pollen-grains to the 

 stigma, when the pollinia are transported by insects 

 to another flower; and the anther opens widely in 

 order that the poUinium should be easily withdrawn ; 

 but in the Bee Ophrys, the caudicle, by a slight in- 

 crease in length and decrease in its thickness, and by 



