AND ITS RELATION TO ANIMAL LIFE 127 



nitrogen than a crop wanting in the same. 



So that the cane growers of Natal or else- 

 where, to obtain the maximum of nitrogen in 

 a given green crop, must manure their land 

 with iron phosphates and potash. 



In the chapter on Variation, p. 40, I 

 have quoted an analysis of two sugar-growing 

 soils. If the difference in the iron is so marked 

 in the short span of fifteen years, what must 

 be the condition of millions of acres in Europe 

 and Asia, which have been cultivated for 

 hundreds of years, without ever having had 

 any iron restored to the soil. 



It is evident at once that the majority of 

 the soil in those parts of the world that have 

 been cultivated for centuries must have be- 

 come very deficient, if not entirely wanting, 

 in iron. 



This explains why much of the sugar grow- 

 ing of the West Indies has become unprofitable, 

 and why the important crop turnips in Eng- 

 land has decreased so in late years. See The 

 Field of November 3, 1900. 



The absence of iron from rice, to which I 

 have already referred, is perhaps a crucial 

 instance. 



