124 PLANT DISEASE 



preponderance of silica in it ; therefore, if the 

 wheat plant could have all the silica it re- 

 quired it would be hard, especially as the ash 

 of the straw should contain about 70 per cent, 

 of silica. 



3. Professors Vogel, Grandean, and Storer 

 all agree that humus is a solvent of silica. 



4. Storer lays particular stress on the value 

 of humus to soils that are naturally too dry. 



5. In Japan the wheat straw is very strong 

 and rust is practically unknown ; it also has a 

 very humid climate and soil. (The above is 

 quoted from the printed report of the Rust in 

 Wheat Conference held in Adelaide in 1892.) 



6. Australia, and for that matter, South 

 Africa, are the very reverse of Japan in climate, 

 being very dry, and there is a great deficiency 

 of humus in the soils of both countries. 



Therefore I claim that as there is a defi- 

 ciency in the soil, the wheat plant cannot take 

 up all the silica it requires, and, as far as I 

 am aware, the only practical way of applying 

 humus to the soil is by ploughing in a green 

 crop, which according to Storer is largely in- 

 fluenced by its quality, by so doing the rust 

 fungus will be defeated, that is, if the green 



