THE GEOGRArHICAL DISTRIIJUTIOX OF PLANTS. 113 



Secondly, in the Southern hemisphere, we have a very simi- 

 h\r, though much less abundant Anlarciic-alpine Flora, which 

 is found near the sea level on the islands of the southern ocean, 

 and extends northward upon the mountains of Ghili, Australia, 

 Tasmania, and New Zealand, and even up to Borneo. The 

 phenomena of distribution of this Flora are so similar to what is 

 found in the Northern hemisphere that it is believed its distribu- 

 tion can be best explained by a southern glacial period. 



Proceeding next to Temperate regions, we find a most marked 

 contrast between the northern and southern hemispheres. In the 

 former we find the plants, the ordinary trees, shrubs, and herbs 

 which we all know, all across Europe, Asia, and America, are 

 much alike in character, and the differences between the plants of 

 different regions is rather one of relative richness or poverty in 

 forms than of differences in the forms tliemselves, — a point which 

 I will refer to" again immediately. Hence, with the exception of a 

 specially rich assemblage in the Caucasian and Western Meditera- 

 neau region, all the plants of the northern temperate zone are 

 grouped into one Plora called the Intermediate or Temperate 

 Flora, and the rich exception of which I speak is appropriately 

 called the Mediterraneo Caucasian Flora. This latter is exceed- 

 ingly rich in species, six-sevenths of those of Europe belonging to 

 it. Now the uniformity of this Northern Temperate Flora is very 

 fully explained b}^ what is known of its history. Around the 

 Arctic ocean, at several points, in Greenland, Spitzbergen, Siberia, 

 and other places, there are found abundant fossil deposits of 

 plants in Tertiary rocks, which fossils are undoubtedly the 

 remains of the ancestors of our living north temperate vegetation. 

 Not only are the species of fossil and living forms very similar, 

 but in manj' cases they appear to be identical. Our North Tem- 

 perate Flora then, in the Tertiary Period, lived and flourished all 

 around the Arctic circle and within it, and probably extended to 

 the pole itself. Then great climatic changes drove it southward, 

 and it peopled all f^urope, Asia, and America with a similar flora. 

 This was subsequently driven to the south by the Glacial period, 

 as we have noticed, and in the changes attendant upon that 

 process and its return northward, parts of it suffered severely. 

 Thus, in Europe, this flora is for the most part a poor one, having 

 far fewer species than our own. This is explained doubtless by 

 the fact that in Europe the mountain ranges run east and west, 



