GEOGRAPHICAL VICISSITUDES OF PLANTS. 299 



the measurement of the response the plants have 

 made to the different physical conditions which set 

 in, it may be, ages ago, and which have determined 

 the habitats of the species ever since. Not unfre- 

 quently the type of the primitive leaf of a genus 

 (and perhaps even of an order of plants) will be 

 revealed in the shapes of the radical leaves, which 

 are nearly always different from the later -formed 

 leaves. In the different species of Buttercups these 

 radical leaves are remarkably alike, and in striking 

 contrast to the variable patterns of the leaves charac- 

 teristic of different species. 



In the northern hemisphere, and for the matter 

 of that in the southern hemisphere also (although 

 the two periods may not have been contemporane- 

 ous, but successive), the most remarkable of all the 

 geological epochs, with the exception of the Miocene, 

 for abounding vegetation, was the Carboniferous. 

 But if we compare the flora of these two widely- 

 separated epochs we cannot help being struck with 

 their contrast. The Carboniferous flora abounded 

 in individuals. Its . character was extremely mono- 

 tonous. It is doubtful whether true flowers (with 

 the exception of those of the Coniferae) had then 

 appeared, for Antholites is now degraded from its 

 supposed rank as a fossil Aroid to a species of 

 Horsetail. Palms, once supposed to have been 

 present in some abundance, are now known to have 

 been few, and some botanists doubt the genuineness 



