400 THE SELF-FERTILIZATION OF PLANTS. 



efficiency in the working of the mechanism. The 

 pollen-mass does not slip, of itself, from the anther- 

 cells but requires force, ab extra, to be torn therefrom. 

 Were the anther-cells and the pollen-mass to proceed a 

 little further in their development, so as naturally to 

 disengage the latter from the meshes of the former, 

 the flower could well be self-fertilized, by means of the 

 very beautiful adaptations which facilitate the action 

 of insects. 



Now, this is the case with one of the species of 

 Orchids, and such species, so self-fertilized, is excep- 

 tionally fertile and vigorous ! 



" Robert Brown," says Darwin (p. 65, "Fertilization 

 of Orchids "), " first observed that the structure of the 

 Bee Ophrys is adapted for self-fertilization. When 

 we consider the unusual and perfectly adapted length, 

 as well as the remarkable thinness, of the caudicles of 

 the pollinia; when we see that the anther-cells naturally 

 open, and that the masses of pollen, from their weight, 

 slowly fall down to the exact level of the stigmatic 

 surface, and are there made to vibrate to and fro by 

 the slightest breath of wind, till the stigma is struck ; it 

 is impossible to doubt, that these points of structure 

 and function, which occur in no other British Orchid, 

 are specially adapted for self-fertilization." 



Now, although the different species of Orchids have 

 certain specific differences of structure, they were origi- 

 nally all capable of self-fertilization; and it has been 

 but a slight modification of their structure, which has 

 deprived them of such capacity. Did space permit, it 

 would be possible, to take up each species, and point 

 out the modification mentioned. In the first species, 

 mentioned by Darwin, the failure of the flowers to 



