240 Plant Life and Evolution 



very humid climate, which seems to have character- 

 ized most of the Carboniferous. There seem to have 

 been two great land masses in existence, a northern 

 and a southern one, and the floras of the two were 

 different in many ways. Thus the Southern Hemi- 

 sphere was characterized by a type of fern, Glossop- 

 teris, which was accompanied by a number of 

 other peculiar southern types (see Scott: " Studies 

 in Fossil Botany"). It was probably during this 

 transition period, between the Carboniferous and 

 the early Mesozoic, that the modern cycads and 

 conifers first became prominent. These plants are 

 most of them more or less xerophytic, and the in- 

 creased aridity of the climate of this period may 

 very well have been the cause of the ascendency of 

 these plants over the moisture-loving pteridophytes 

 of the preceding geological epoch. 



The Highest Types of Plants Arose in the Meso- 

 zoic. The second great geological epoch, the Meso- 

 zoic, is supposed to have been of much briefer dura- 

 tion than the Paleozoic, but it is noteworthy as the 

 time in which the highest groups of plants and ani- 

 mals came into existence. Birds and mammals, on 

 the one hand, and the angiospermous flowering 

 plants on the other, made their appearance during 

 the Mesozoic. The warm but dry climate of the 

 early Mesozoic seems to have been especially favora- 

 ble to the cycads, which at that period reached their 

 culmination, giving place later to the more modern 

 conifers and angiosperms. During the latter part 



