inches across, while the little popgun elder of the 

 East is supplanted here by a species 1 2-20 inches 

 in diameter. 



Most of the trees mentioned are indigenous to 

 California and three-fourths of them are found 

 only in that state. Why this great prodigality of 

 Nature in behalf of the Pacific Slope, and espe- 

 cially of little California? 



The solution of this problem involves a brief 

 discussion of certain controlling factors. 



At the outset we may observe that an impassable 

 climatic barrier is set up at present, by Nature, 

 preventing migration north and south. The Torrid 

 Zone, in which no resinous trees can grow except 

 on high peaks, separates the world's forests into 

 unequal and very different floras. 



The Southern Hemisphere is the home of the 

 Araucaria, the Eucalyptus and the Acacia, while in 

 the Northern Hemisphere are found in addition 

 to the hosts of broad-leaved, non-resinous trees, 

 such as oak, ash, hickory, etc. all of the large 

 families of pine, larch, cedar, spruce, and fir, with 

 the redwood, cypress, and juniper; the distribution 

 of these trees across the two continents, however, is 

 very unequal. 



DISPARITY OF AREAS AND DISTRIBUTION. 



The northern part of the eastern continent 

 Eurasia is approximately 9,000 miles across. 

 North America is but 3,000. We would naturally 

 expiect, for instance, three times as many pines in 

 Eurasia as in America. Just the reverse is the 

 case. Of the 80 species of known pines only 20 



(4) 



