THE VIRGIN FOREST 



Thus Rio de Janeiro is hotter than Pernambuco and Colombo, 

 although the capital is on the southern border of the tropical zone, 

 while Pernambuco and Colombo are only 8° respectively south 

 and north of the Equator. And Berlin shows a higher temperature 

 than either of these tropical cities. 



A second table shows the mean temperatures of the hottest months : 



Pernambuco 80 • 8° 



Colombo 81 -3° 



Rio de Janeiro 79 • 9° 



But while in Leipzig and Berlin the temperature in the coldest 

 months may fall to zero Fahr., in Pernambuco the mean tempera- 

 ture of the coldest month (July) is 75°, and the minimum temperature 

 of the year is 64-9°. In Rio the mean temperature of the coldest 

 month is 70-1 °, whereas in eastern Germany the mean temperature 

 is below the freezing-point, and in western Germany only three or 

 four degrees above freezing-point. We see, then, that the essential 

 difference does not consist in the higher temperature of the tropics, 

 but in the fact that the tropics are distinguished by a uniformly high 

 temperature. The variation in the course of the year averages less 

 than 18°, whereas in Europe it averages 86°! Consequently a table 

 of mean annual temperatures reveals the real nature of the difference : 



Rio de Janeiro 74 "8° 



Pernambuco 78*2° 



Berlin 48-3° 



In the temperate zones we have a warm and a cold season in sharp 

 contrast, whereas in the tropics it is summer all the year. Our 

 plants have to reckon with a winter which brings their growth to 

 a standstill or kills them completely. For the life-process needs 

 warmth for its operations, and owing to the large amount of water 

 contained in plants — and their stems, rich in sap, may contain as 

 much as 96 per cent, of water — the whole body of the plant becomes 

 rigid if the thermometer sinks below freezing-point. 



Now what is the natural consequence of the fact that whereas 

 our plants are actively living only for a few months in the year, 

 the tropical plants are active all the year through? It is obvious 

 that a tree which has hardly half the year at its disposal must work 

 twice as hard as a tree whose life knows no interruptions. The organs 

 of the plant which, like a chemical laboratory, with the help of 

 the sunlight and the water rising from the roots, manufacture the 

 materials needful for further growth, are, as we know, the leaves. 



E 65 



