i9i4-] SOUTHEASTERN NORTH AMERICA. 141 



ical marine faunas : that plants reflected their environment in the 

 past as in the present. 



A considerable number of botanists love to dwell upon the temer- 

 ity of their paleobotanical friends in venturing to determine leaf 

 impressions. I admit at the outset that some determinations are 

 much too sanguine, especially when based upon fragmentary mate- 

 rials. There is more or less convergence in foliar characters in 

 unrelated or remotely related families and there is also considerable 

 variation in the leaves of a single species, but the fact remains that 

 foliar characters in general are more conservative than those derived 

 from almost any other organs of plants. They are subjected to less 

 complex environmental factors and always have been. It should be 

 remembered that characters less essential in the vital activities of 

 plants, such as leaf form, when once acquired, may continue practically 

 unchanged for thousands of years and afford a surer clue to relation- 

 ship than characters more immediately within the field of action of 

 natural selection. This is shown by the persistence of fern fronds 

 on the Paleozoic Pteridosperms ; by the uniformity of Cycad-like 

 fronds from the Permian to the Cretaceous ; and by the striking per- 

 sistence of dicotyledonous foliar types from the Mid-Cretaceous to 

 the present. It is paralleled by Dall's observations on the persistence 

 of superficial and ornamental shell characters in the Mollusca from 

 the Cretaceous to the Recent. 



The opinion I mention in a preceding paragraph is mainly the 

 result of ignorance both of foliar characteristics and paleobotanical 

 literature, and an unwillingness to spend the time necessary for a 

 mastery of the subject. I have tested systematic botanists time and 

 again with recent leaves and the results are not especially creditable. 

 They generally know that leaves are green in color and that some are 

 simple and others compound : they may even know whether the mar- 

 gins are entire or toothed, but the venation is usually a closed book. 

 I know of but one manual that pretends to pay careful attention to 

 foliar characters and that is Sargent's " Tree Book " and even here 

 the figures pay no attention to venation. 6 In the tropics where 

 flowers and fruits are often unobtainable or beyond reach it is easy to 



G Sudworth's "Trees of the Pacific Slope" is the most admirable work 

 in this respect that has ever been published. 



