THE MOVEMENTS AND HABITS OF PLANTS. 19 



verse functions — often of trifling importance compared 

 with their proper function — converted other organs into 

 mere purposeless rudiments, and arranged all as if they 

 had to stand separate, and then made them cohere ? Is 

 it not a more simple and intelligible view that all the 

 Or ch idea owe what they have in common to descent 

 from some monocotyledonous plant, which, like so many 

 other plants of the same class, possessed fifteen organs, 

 arranged alternately, three within three, in five whorls ; 

 and that the now wonderfully changed structure of the 

 flower is due to a long course of slow modification — each 

 modification having been preserved which was useful to 

 the plant, during the incessant changes to which the or- 

 ganic and inorganic world has been exposed ? 



SPECIAL ADAPTATIONS TO A CHANGING PURPOSE. 



Fertilization It has, I think, been shown that the Or- 



of Orchids, chidew exhibit an almost endless diversitv of 

 pa^e 28° . 



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 pur- 

 pose becomes adapted by slow changes for widely differ- 

 ent purposes. To give an instance : in all the Ophrem, 

 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 pollinium 

 should be easily withdrawn ; but, in the Bee ophrys, the 

 caudicle, by a slight increase in length and decrease in its 

 thickness, and by the anther opening a little more widely, 

 becomes specially adapted for the very different purpose 



