184 Plant Life and Evolution 



distributed by insects, and Welwitschia, one of the 

 gymnosperms, but possibly allied to the angio- 

 sperms, is supposed to be entomophilous. Most of 

 the plants whose organs have been modified with 

 reference to animal structures are angiosperms, and 

 the extraordinary variety of flowers and fruits is 

 doubtless due in a large measure to such adaptations. 



Which is the older of the two main divisions of 

 angiosperms must remain for the present in doubt. 

 The geological record is very unsatisfactory on 

 this point, and comparative morphology gives 

 hardly any more certain answer. It is possible, at 

 least, that the divisions into monocotyledons and 

 dicotyledons is a somewhat artificial one ; and it may 

 be that from an indifferent primitive stock, angio- 

 sperms in all essential respects, a number of lines 

 arose, some to become monocotyledons, others di- 

 cotyledons. 



The question as to the nature of the primitive 

 angiospermous flower is also not at all satisfactorily 

 settled. While some of the diclinous floral types 

 can be explained as reduced from hermaphrodite 

 ones, it is by no means always the case, and we be- 

 lieve that some, at least, of these diclinous types, 

 are really primitive. This implies that before 

 monocotyledons and dicotyledons were established 

 as such, both types of flowers had developed, 

 and these in the further course of evolution were 

 transferred to both monocotyledonous and dicoty- 

 ledonous families. 



