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THE AMERICAN NATURALIST [Vol. L 



woody forms, the Angio sperms must have been in the 

 process of evolution for a period many times as long as 

 that since the origin of herbs, evidently beginning at a 

 date far earlier than that at which the first angiospermous 

 fossils occur. 



This conclusion is still further strengthened by other 

 facts. The earliest fossil Angiosperms seem to have been 

 trees, presumably the most slowly alterable type of all. 

 Furthermore, whatever may have been the importance in 

 recent times of hybridization through cross-fertilization 

 by insects as a cause of accelerated evolution, this factor 

 was evidently inoperative at the origin of the Angio- 

 sperms, since, according to Handlirsch, flower-loving in- 

 sects did not make their appearance till the Tertiary. 

 The specialized character and apparently high phyloge- 

 netic position of many of the earliest fossil Angiosperms 

 also renders it highly probable that they were the product 

 of a long evolutionary history. 



Evidence from all sources therefore seems to agree that 

 the origin of these higher seed plants took place at a time 

 very much earlier than their paleontological record indi- 

 cates. That they were not preserved as fossils in hori- 

 zons lower than the Cretaceous is perhaps due to the fact 

 that the earliest Angiosperms, as Professor Bailey and 

 the writer have suggested, 7 appeared under essentially 

 temperate climatic conditions, which in the Mesozoic were 

 mainly confined to upland regions where fossilization 

 would take place much less commonly than in lowlands. 

 This apparent predilection of these primitive Angio- 

 sperms for an environment cooler than the tropical, to- 

 gether with what we have noted as to their high antiquity, 

 suggest that the refrigeration of climate which took place 

 in the Jurassic might have been a factor in their origin; 

 and even tempts one to look farther back toward the 

 epoch of markedly low temperatures subsequent to the 

 close of the Paleozoic, which caused so many radical 



TSinnott, E. W., and Bailey, I. W., "Foliar Evidence as to the Ancestry 

 II, 1915, pp. 1-22. V r0Iiment ° f ^ An g 10& P erms ' 



