140 PLANT DISEASE 



go into a South African orange grove which 

 is not suffering from chlorosis. 



It is evident even to an ordinary observer, 

 for you will see the young leaves quite yellow, 

 and sometimes the top half of a large tree 

 yellow, and it is quite common for farmers to 

 tell you they are losing several trees per year, 

 but they cannot understand they are dying 

 from poverty. 



/There is another important feature about 

 these chlorotic trees.! 



" /They will be found as a rule to be covered 

 with muscle scale, and if they are not it will 

 be because they have been fumigated. You 

 will also find the fruit of chlorotic trees very 

 deficient in sugar in fact, the juice of an orange 

 of such a tree is neither sweet nor sticky as 

 it should be. 



As the sugar is distinctly a carbon com- 

 pound, and the carbon is controlled by the 

 chlorophyll, it follows as the sugar is defec- 

 tive so is the chlorophyll. 



Therefore manure to cure the chlorosis, and 

 you will produce a fine sugary orange ; that is, 

 providing there are other necessary consti- 

 tuents present, like potash, which has the 



