62 EVOLUTION 



in the southern continents. At last the great ice-sheet 

 descends over Europe and North America, and as it 

 melts away the temperate plants creep up from 

 the south and clothe our latitudes with its familiar 

 vegetation. 



This broad glance at the evolution of the plant world 

 as a whole must suffice for the purpose of our brief 

 story. The transformation of the leaves of the higher 

 plant into sex organs and flowers would take us beyond 

 our limits, and the many questions of the relationship of 

 the different types are too controversial and technical to 

 discuss here. The links may one day be found in strata 

 that are not yet uncovered, and indeed botanists find a 

 large number of transitional features in the early 

 representatives of all the chief groups. We pass on to 

 the more interesting study of the evolution of animal 

 forms, which will bring us to the consideration of man's 

 own development, 



