CLIMATIC ZONES 23 



widely separated by great ocean barriers, while at the north, the 

 two great continental masses, Eurasia and North America, are 

 almost joined by a chain of islands, evidently indicating an even 

 more complete connection in not very remote geologic time. 



The great antarctic continent, completely isolated, and ice 

 covered from the lofty mountains to the sea, is practically destitute 

 of vegetation. 



Very different are the conditions in the arctic regions, where 

 far beyond the arctic circle in Greenland, Spitzbergen and Alaska, 

 there is an abundant flora which develops rapidly during the long 

 days of the brief summer. 



Owing to the absence of any great barriers, we find that the 

 vegetation of the higher latitudes in the northern hemisphere is 

 relatively uniform, many species occurring throughout the range, 

 so that the floras are very much alike in Scandinavia, Siberia and 

 northern Canada. 



There is no true antarctic flora, and the austral flora is much 

 less developed than the corresponding vegetation of the north. 



The austral or sub-antarctic flora is best developed in South 

 America, but is also found in New Zealand and southern Australia 

 It is quite absent from South Africa. 



The sub-arctic flora merges insensibly into that of the north 

 temperate zone, which has much the same general character 

 throughout Eurasia and North America. 



Conditions in the temperate regions of the southern hemisphere 

 as already stated are very different and owing to the extreme 

 isolation of South America, South Africa, and Australia, their 

 floras are very different. It is true that there are certain corre- 

 spondences pointing to former more intimate connection of the 

 land-masses, than now exist; but the differences in the vegetation 

 far outweigh the resemblances, and each of the three regions has 

 an extremely individual flora, indicating a very long period of 

 isolation. 



Comparing the floras of the northern and southern hemispheres, 

 especially in the temperate regions, it is evident that certain 

 families and genera are either confined to one or the other, or that 

 they predominate to such an extent as to make it pretty certain 

 that they originated there. Thus the oaks, maples, elms, birches, 

 poplars, sycamores, are almost exclusively northern, and the same 



