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THE AMEBIC AN NATURALIST [Vol.L 



have unquestionably been the progressive cooling of our 

 earth's surface, as well as those recently recognized sec- 

 ular periodic twilights of the sun god, known as glacial 

 periods. The latter have worked in an exterminating 

 manner and have wiped out well nigh completely whole 

 types of plants and have left the way clear for the unre- 

 stricted development of better adapted forms. For ex- 

 ample, at the end of the Paleozoic, in the late Permian, 

 we find world-wide evidence of glaciation, which resulted 

 in the virtual extinction of the great cryptogamic forests, 

 which contributed the raw materials of our most abundant 

 coals. With the passing of the arboreal Cryptogams, the 

 Gymnosperms became the predominant element of the 

 world forests in the Mesozoic. At the end of the Creta- 

 ceous there was another age of extinction, which wiped 

 out the mass of Gymnosperms and particularly the Coni- 

 fers. The naked seeded plants, which prevailed in the 

 medieval period of our earth's history, have in the vege- 

 tation of to-day been reduced in the number of species to 

 the merest fraction of seed-producing plants; which in 

 the present age are overwhelmingly angiospermous. 



From the present standpoint, however, the progressive 

 but not spasmodic cooling of our earth is of even greater 

 importance. Investigations initiated in my laboratories 

 have made it clear that herbaceous Angiosperms have 

 been derived from woody ones as a response to the in- 

 creasing coldness of terrestrial climates. Plants of this 

 organization are of such efficiency that they are able to go 

 from seed to seed in a few weeks and thus pass through 

 the inclement winter season in a resting stage. The orig- 

 inal researches in this direction were undertaken by Pro- 

 fessor Eames. The theme in the past two years has 

 undergone a profitable exploitation by other former stu- 

 dents in both botanical and geological publications. The 

 origin of the herbaceous type in the Angiosperms has in 

 itself added a notable impetus to the rate of evolution in 

 the group. Whatever hypothesis one adopts as to the 

 mode of the origin of species, it is quite clear that the 



