204 THE CHAIN OF LIFE. 



give great support to the doctrine of gradual transformation of 

 species. Farther facts and farther comprehension of the dif- 

 ference between species and races will be necessary to the 

 settlement of these questions. In the meantime it would 

 appear that the Jurassic flora rapidly gave place, at a particular 

 point of geological time, to that of the modern world, and 

 this not merely in one locality, but over the whole northern 

 hemisphere ; and there are apparently similar facts in the 

 southern hemisphere as well. It farther appears that each genus 

 was at first represented by many species, and that as time went 

 on these were gradually reduced to a few best suited to 

 survive ; and that the changes of climate and level which 

 occurred distributed these over different parts of the con- 

 tinents in a way at first sight very anomalous, but which Prof. 

 Gray somewhat quaintly represents as follows : — 



" It is as if Nature, when she had enough species of a 

 genus to go round the four floral regions (Europe, East Asia, 

 West America, and East America), dealt them fairly one at 

 least to each quarter of our zone ; but when she had only two 

 of some peculiar kind, gave one to us, and the other to Japan, 

 Mantchuria, or the Himalayas ; and when she had only one, 

 divided it between the two partners on the opposite sides of 

 the table." 



Lastly, it seems very probable that many so-called species 

 are nothing more than varietal forms, which may very well 

 be modified descendants of Miocene or Eocene plants now 

 figuring in our lists under different names. 



