158 PLANT DISEASE 



It follows that in time the soil must become 

 very impoverished in this mineral, to say 

 nothing of the other mineral constituents. 



This view of the case appears to me to be 

 much more practical, and more within the 

 lines of common sense, than to suppose that 

 the phylloxera causes a diminution of potash. 



And as Professor Hilgard says 



" Potash with nitrogenous manure would 

 mitigate the effect on the vine produced by 

 phylloxera, has been verified by experience." 



If the vines had been manured with plenty 

 of iron, some potash and phosphates, I have 

 not the least doubt no such thing as phylloxera 

 would ever be heard of ; for the reason that 

 the vines would be so healthy and full of 

 chlorophyll matter as to give these aphides 

 not a trace, but a large dose of this chemical 

 compound which, instead of being a food, 

 would be a poison to this insect. 



I have now pointed out that there are forms 

 of insect life that are to all intents and pur- 

 poses simply an extension of the fungi. Nor 

 is the list of these insect pests exhausted, for 



