The Angiosperms 173 



Among the Choripetalse there are much greater 

 differences of structure than among the Sym- 

 petalae, which are reducible to a comparatively 

 small number of types, although in point of num- 

 bers they probably surpass the Choripetalse. It 

 is among these highly specialized Sympetalae that 

 we meet with the most successful types, these being 

 the dominant dicotyledons, especially in the tropics. 



The largest family of angiosperms and the one 

 which, on the whole, seems to have succeeded best 

 in the struggle for life, is the Composite. The uni- 

 versal distribution of Compositae and the aggressive 

 character of many of them are sufficient proofs of 

 the efficiency of this type. This superiority seems 

 to be more or less due to their extraordinarily per- 

 fect devices for the transportation of their seeds. 

 The numerous wind-borne seeds of the dandelion 

 and thistles, the tenacious burs of the bur-marigold 

 and burdock, together with the robust constitution 

 of the plants themselves, have given these weeds an 

 enormous advantage in the struggle for existence; 

 and we see them scattered over vast tracts of coun- 

 try, taking possession of the vacant ground almost to 

 the exclusion of the plants originally inhabiting 

 them. 



Evolution of the Flower in Monocotyledons and 

 Dicotyledons Much Alike. The evolution of the 

 flower has followed very much the same course in 

 monocotyledons and dicotyledons, and illustrates 

 once more the remarkable similarity that may result 



