126 PLANT DISEASE 



illustrating how the soil has become impov- 

 erished. 



It has been proved by analysis that a small 

 percentage of iron is extracted from the soil 

 in every crop of cane sugar grown, so it would 

 not take many years to withdraw a fair per- 

 centage of this mineral from the soil, as it is 

 an important factor in chlorophyll, and the 

 sugar of the plant being governed by the 

 chlorophyll, as the iron is withdrawn from the 

 soil, so must the yield of sugar decrease. 



The cane growers of Natal are paying atten- 

 tion to the restoring of nitrogen to the soil 

 by growing leguminous crops and ploughing 

 them in, but the question of returning iron to 

 the soil is not recognized as necessary, yet its 

 restoration is just as necessary, not only for 

 the production of sugar, but also for the growth 

 of the leguminous crop, as I have previously 

 shown. 



One thing is certain that a normal plant 

 is in a much better position to perform its 

 natural functions than a chlorotic one, there- 

 fore it is reasonable to assume that a legu- 

 minous crop containing all the mineral con- 

 stituents will be in a better position to assimilate 



