THE COURSE OF BIOLOGIC EVOLUTION. 33 



history of plants shows that it was not until this combination 

 occurred that the great revolution in the vegetable world was 

 brought about. 



Exogenous Angiospermy . — The time came at last, we know 

 not at what precise period, when exogenous plants acquired a 

 closed ovary. This is the highest type of vegetation yet 

 reached, and the proofs of its potency confront us every time 

 we behold a modern forest of dicotyledonous trees. The great 

 variety, beauty, strength, and grandeur of this now dominant 

 vegetation amply attest the efficacy of exogeny combined with 

 angiospermy in the attainment of vegetal perfection. Yet the 

 time that elapsed from the beginning of either of these ad- 

 vances, taken alone, to that at which their fortunate combina- 

 tion took place was enormous. Not in the great coal period 

 nor its closing Permian stage ; not in the Trias which suc- 

 ceeded did there come forth a single exogenous plant whose 

 germ was thus protected. The great and abundant fossil 

 floras of the Rhetic and Lias of India, Australia, Bavaria, 

 Sweden, and their near equivalents in Virginia and North 

 Carolina, the Connecticut valley, and in both Old and New 

 Mexico, have none of them yielded a trace of any such plant. 

 The same is true of the equally abundant Oolitic floras of York- 

 shire, France, Italy, Siberia, and Japan. Not even the highest 

 Jurassic strata of any part of the world have with certainty 

 produced an exogenous angiosperm. The oldest formation at 

 which such plants occur is that on which our own cit)-, the 

 nation's capital, stands, viz., the Potomac formation, whose 

 geological position is doubtful as yet, but if Jurassic, centainly 

 represents the extreme uppermost part of that system. By the 

 author of its flora, Professor Fontaine, it is regarded as the 

 equivalent of the Wealden, which is now commonly supposed 

 to be the fresh water equivalent of the Neocomian or lowest 



