GEOGRAPHICAL DISTRIBUTION OF ORGANISMS. 



473 



warm temperate zone; then a region of deciduous hard- 

 wood trees, corresponding with the full temperate zone; 

 then a region of conifers and birches, corresponding to 

 the cold temperate or subarctic zone; then a treeless 

 region, corresponding to the arctic or circumpolar zone; 

 and finally a plantless or nearly plantless region, occupied 

 by the polar ice cap (Fig. 332). 



Qualification. — 1. By the terms region of palms, 

 region of pines, etc., we mean only that these kinds of 

 trees by their abundance give character to the aspect of 

 field and forest. 



2. We have drawn lines separating these regions, but 

 in fact they shade completely into one another. 



3. We have drawn 

 the separating lines 

 regular, like lines of 

 latitude, but, in fact, 

 they are irregular, 

 like isothermal lines. 



Regions in Al- 

 titude. — These re- 

 gions being tempera- 

 ture regions, similar 

 regions are found in 

 ascending mountains 

 (Fig. 332). A moun- 

 tain in the tropics if 

 it reaches perpetual 

 snow will contain all 

 of them, while moun- 

 tains in higher lati- 

 tude only the higher 

 portions of the se- 

 ries. For example, in the Peruvian Andes we have all 

 these regions successively encircling the mountain — 





<T- 





2 







tf- '"{ 







3- -f 



\*"***'^^ 





x.~—k. 



h^ 2 





\v\ 3 



A 



/ 



1 A 



3 r(\ 













Fig. 332. — Diagram showing temperature 

 zones in latitude and corresponding zones 

 in altitude : 1, tropical ; 2, temperate ; 3, 

 subarctic ; 4, arctic ; 5, perpetual snow. 

 a, b, c, mountains in tropical, temperate, 

 and subarctic regions respectively. 



