170 THE PRINCIPLES OF 



Now allow me to point out that in these experiments on 

 wheat and barley the word " silica " does not occur. How 

 is it, I should like to know, that in all examination papers 

 which come into my hands a preponderating importance is 

 attached to silica ? There must be some fundamental error 

 at the base of this, for it goes through hundreds and thousands 

 of answers. I am told that silica is the thing to give wheat, 

 and it is silica which is laid stress upon as necessary for 

 corn. It is a very odd thing, and it reminds me of a 

 story by our old friend Dr. Voelcker, in which he related that 

 a farmer exclaimed with reference to an analysis of soil in 

 which some 80 per cent, of insoluble silica was recorded " My ! 

 what a grand thing that inzoluble zilica must be for the 

 ground." I see little in the Rothamsted results as. to the 

 effects of silica. I never doubt any ground containing a 

 sufficient supply of silica of course it does; and there must 

 be some grave error in the teaching of boys all over the 

 country when they rush to silica at once as the most 

 important constituent you have to add to your corn crops. 



With reference to turnips and swedes and mangel wurzel, 

 one of the most extraordinary lessons bearing upon practical 

 farming is this without manure you get no root crop. It 

 is a very significant fact, and bears out what I have already 

 stated, that root crop cultivation is the most difficult, most 

 complicated, and most expensive of all tillages. In turnip 

 cultivation one of the most extraordinary facts is the imme- 

 diate and rapid effects of superphosphates. Here the deficient 

 material is not nitrogen, but phosphorous. The mineral 

 constituents seem to be wanting in the case of the turnip 

 crop. I cannot help thinking that this is due to the peculiar 

 cultivation of these roots, and the period during which they 

 are growing. Turnip cultivation requires" the ground to be 

 thoroughly tilled to a great depth, and to be in a fine con- 

 dition, the very condition in fact for nitrification to be going 



