r> 



AND ITS RELATION TO ANIMAL LIFE 155 



with the constituents necessary for the pro- 

 duction of a normal chlorophyll. 



If such crops are immune, then two points 

 will have been proved : first, that a crop grown 

 on a normal soil is immune to locusts ; and 

 secondly, that these insects are an extension 

 of the fungi. 



If crops so grown prove to be immune to 

 locusts, we are already far along the road 

 to prove that the ravages of insects and fungi 

 are due to the same cause and can be 

 counteracted by identical or at least similar 

 remedies. 



In the aphides we have another class of 

 insect, where at least a trace of chlorophyll is 

 recognized. The phylloxera of vines and the 

 aphis of apple trees are two well-known insects 

 of this class, and any observer must have 

 noticed that apple trees attacked by this 

 disease always have a very dark bark, and 

 not a green bark like one containing chloro- 

 phyll. 



An interesting point in connexion with this 

 fact is that lime plays an important part in 

 this disease, for it is proved by analysis that 

 trees attacked by this disease are very deficient 



