INTRODUCTION 9 



floras which survived for some time later in the northern hemi- 

 sphere. This separation of a northern and southern flora ifi signifi- 

 cant, as probably something analogous took place a1 a later period, 

 resulting in the marked differences now existing between the 

 temperate floras of the northern and southern hemisphere 



With the opening of the Mesozoic seed-bearing plants in- 

 creased in numbers and importance, but were all "gymnospenrj 

 i. e., forms with exposed seeds, like those of the living coniferous 

 trees. The latter were represented by forms allied to the Arau- 

 carias and Kauri pines of the southern hemisphere, and the cycads 

 and Ginkgo of the present day. The cycads are palm-like woody 

 plants, with less than 100 species at present, inhabitants of tin- 

 tropics and warm temperate regions. The only existing repre- 

 sentatives in our territory, are two small species of Zamia in 

 southern Florida. 



Ginkgo biloba, the curious "maiden-hair tree," not infrequently 

 seen in cultivation, is the sole survivor of a large order of tn 

 which flourished in the early Mesozoic. The living species has 

 been found wild in western China, but has been cultivate. 1 in 

 China and Japan for a very long time. 



The cycads reached their culmination in the middle of its 

 Mesozoic (Jurassic) when they were a predominant feature 1 of the 

 vegetation. The most specialized forms had flowers suggesting 

 those of some of the higher flowering plants, and it has even been 

 thought that these (Angiosperms) may have originated from 

 some of the Jurassic Cycadophytes. In the Jurassic are found 

 also the beginning of the modern coniferous genera, pine-, cy- 

 presses, cedars, etc., and the first sequoias are probably of about 

 the same age. With the establishment of the modern conife 

 the cycads become much less important and only a few of the !• 

 specialized genera have survived to the present day. 



The last period of the Mesozoic, the Cretaceous, is notable ai 

 period of extraordinary development of new life-forms, both plant 

 and animal. The vegetation indicates a moisi warm uniform 

 climate, due, perhaps, in part to extensive invasions of the land 

 by the oceans. 



In the Cretaceous are found for the fust time unmistakable 

 remains of angiosperms, the modern type of seed-bearing plai 

 These are first encountered in the lower Cretaceous, where they 



