192 DISEASES OF PLANTS ILLUSTRATED IN THE TOTATO MURRAIN. 



beforeliaiid. I shall merelj' hazard the following indication 

 without attributing too much value to it, since the rotation de- 

 pends not entirely on the chemical circumstances attendant on 

 nutrition, but perhaps quite as much on the state of aggregation 

 in which the soil is left by particular crops, as also on the quan- 

 tity of Immus it may contain. The proportions are again ar- 

 ranged in a tabular form for the sake of easy comparison : — 



In the case of wheat, the residue of manure after harvest is in 

 th(! same unfavourable condition for the culti^'ation of potatoes 

 as wood ashes, as appears from the former Table, while in that of 

 rye the result is decidedly favourable. 



Most agriculturists agree that rye is most fitted for newly ma- 

 nured land, which is clearly attributable to its greater amount of 

 phosphoric acid. The best rotation then seems to be to begin 

 with winter lye, and to let potatoes follow. I do not, however, 

 give this as a decided fact ; all I would assert is, that the place 

 usually given to potatoes is the worst and most destructive. 



The choice, however, of another system, if it is to lead to the 

 desired result, must not merely be tried by individuals ; but the 

 earlier methods of cultivation must be abolished, at least as ge- 

 nerally as they have been hitherto firmly established. But 

 unhappily in the very nature of things, any legislative measures 

 can have no effect, even supposing tlie views I have developed 

 to be true. The only measure which a government can take, is 

 to provide by every means at its disposal for the instruction and 

 enlightenment of cultivators, so that on the one side they may 

 possess such well-grounded knowledge of natural science as may 

 enable them to comprehend facts in their just connexion or as 

 actual experience, instead of opposing raw empiricism or the 

 mere observation of facts with the self-sufficiency of ignorance 

 to scientific discussion, and on the other side landowners may 



