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CHAPTER III. 



TRACES OF UNITY IN THE VIVIFYING POWER 

 OF LIGHT AND HEAT. 



THE life of plants and animals is affected by climate 

 and season in a way which shows very plainly that there 

 is the closest connection between vital force and physical 

 force. 



In high northern latitudes, as cold gains the mastery, 

 plant after plant disappears until at last the landscape 

 is almost altogether plantless. 



In the sub-arctic zone which succeeds to the tern' 

 perate region, green pastures, adorned during the short 

 spring and summer with many gay flowers, reach far and 

 wide, and interminable forests of needle trees shut out 

 the prospect in all directions. Oaks have been left 

 behind in the temperate region, but birches and alders 

 and willows struggle on, and their more northernmost 

 outposts are considerably in advance of the lines occupied 

 by the conifers. 



In the arctic zone the trees and in great measure the 

 grassy pastures of the last zone have disappeared, the 

 pastures being replaced by tracts, often of wide extent, 

 covered by sedges and cotton-grass and lichens, the trees 

 by prostrate and tortuous shrubs like those met with in 

 high alpine regions rhododendrons, andromedse, dwarf 

 beeches, alders and willows, bog-myrtles and others. 

 All trees have disappeared, and the place of grass is 



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