280 EFFECTS OF CLIMATE. 



that young plants require, a quantity of these salts 

 is necessary for the ripening of seed ; hence plants 

 require a large supply of inorganic matter from the 

 soil, during the third period of their existence, or 

 during the formation of seed. 



736. These are, in very general terms, the condi- 

 tions requisite to the growth of plants; but there are 

 many special conditions appropriate to particular 

 species, and many important circumstances, which 

 must not be overlooked in studying the chemistry 

 of vegetation. The differences of climate, and their 

 influence on the growth of plants, are not less 

 remarkable than those of the soil itself; and, indeed, 

 the very same soil would possess a very different 

 degree of fertility in different climates. 



737. In the hot moist regions of the tropics, plants 

 grow with far more rapidity, and vegetation is more 

 vigorous, than in temperate regions. In tropical 

 countries, decay proceeds far more rapidly than it 

 does in our own country ; carbonic acid and ammonia, 

 the food of plants, are produced in greater quantity 

 than here ; whilst, from the greater power of the 

 sun, plants are able to assimilate more of those 

 substances than they can in colder countries. 



738. The same circumstances which are favorable 

 to the putrefaction of organic matters, are likewise 

 those which facilitate the decomposition of inorganic 

 compounds in the soil (651). Consequently, in warm 

 tropical climates, a more copious supply of the re- 

 quisite earthy matters is continually being set free, 



