THE COURSE OF BIOLOGIC EVOLUTION. 37 



woods, during Tertian- times, but most of these have small 

 flowers, and in some of the living representatives the lobes of 

 the corolla are cleft nearly to the base, suggesting that at an 

 earlier period in their history they may have really been poly- 

 petalous. The more typical Gamopetalae, with tubular or 

 funnel-form corollas are for the most part unrepresented in the 

 fossil state, and we must regard these plants as among the 

 latest products of development in the vegetable kingdom. 



Nature of Vegetal Development. — I have now endeavored to 

 trace the progress of development in the vegetable kingdom 

 from its earliest beginnings in cryptogamic life to its highest 

 and latest expression in the gamopetalous dicotyledon, with a 

 view especially to showing by what particular steps it has taken 

 place, and how the two laws of the extinction of trunk lino 

 of descent and the persistence of unspecialized types have com- 

 bined to bring about the varied and abundant vegetation with 

 which the earth is clothed. I have sought to emphasize the 

 fact that this evolution has not been in a single ascending .se- 

 ries, that the plants that have one after another succeeded to the 

 mastery have each in turn attained the highest development 

 possible to their respective types of structure and have then 

 surrendered their sceptre forever to the new and more perfect 

 types evolved from them, and have usually dwindled down to 

 comparative insignificance but persisted on in some of their 

 lowest forms. I have wished to make clear and patent the im- 

 portant but rather recondite and popularly little understood 

 truth that biologic progress takes place through this 

 >ympodial dichotomy, and not by true dichotomy, much 

 less by the ordinary monopodial branching represented 

 by the common figure of . a tree. In other words the 

 phylogenetic tree is something considerably different from 

 the common genealogical tree. It further and especially 



