LIFE ON THE EARTH. 13 



tains. The American Flora is richer than that of the 

 old world. If 13000 be the number of phaneroga- 

 mous plants in Tropical America, 4000 may be taken 

 to represent the flora in the Temperate zone. If 

 2000 plants can be collected within a radius of ten 

 miles in India, about 500 can be found in an equal 

 space of the surface of England 1 . 



In Mr Watson's interesting work on the Geogra- 

 phical Distribution of British Plants, we find the 

 Highland plants of Scotland grouped in three divi- 

 sions according to elevation 1000 to 2000 ft., 2000 to 

 3000ft. and 3000 to 4000ft. above the sea. The num- 

 bers are : 



273 species 183 species 85 species 

 48 orders 38 orders 25 orders, 



shewing clearly the reduction of vegetative energy 

 with increased elevation. 



Equally positive is the limitation fixed by climate 

 upon the geographical range of the different natural 

 groups of plants. Proceeding northward from the 

 equator we pass through the fruitful equatorial re- 

 gion of the bananas and palms, the tropical zone of 

 arborescent ferns and figs, the sub-tropical zone of 



1 Humboldt; Hooker, Indian Flora; Watson's British 

 Plants; Balfour's Class Book; Somerville's Phys. Geography, 

 Meyen, Botanical Geography. 



