286 



On the Rotation of Crops. 



agriculturists^ whose desire it is to ascertain facts, and become 

 independent of mere routine. Whatever be thought of the course 

 of cropping indicated by Mr. Blaikie, it will scarcely be doubted 

 that, in proportion as the order of the rotation shall be compre- 

 hensive, and its crops opposed to each other in their physical 

 organization, so will be the economy of the manure, and its energy 

 in promoting vegetation. This I have seen exemplified yearly in 

 the garden, where the minimum of manure, and that composed 

 chiefly of semi -decayed beech-leaves, has produced a great abund- 

 ance of fine vegetables of every description, excepting carrots, 

 which rarely spindle well in a gritty and compact loam. 



The rotation of the garden affords likewise the strongest analo- 

 gical proofs of the theory of the radical exudation. Mr. Pusey 

 has alluded to this theory at p. 12, where he observes that crops 

 of the same kind, following each other, become rapidly less pro- 

 ductive, whether* by exhausting the land of some fertile pro- 

 perty, or by depositing, as has lately been supposed, some excre- 

 mentitious matter injurious to the growth of their own species, 

 though favourable perhaps to the luxuriance of some other 

 tribe/' 



For this theory we are, I believe, indebted to Professor De 

 Candolle, of Geneva ; though Brugmans had previously inti- 

 mated that a certain portion of the juices absorbed by plants were 

 ejected by their roots, after their vessels had separated the saluti- 

 ferous or nutritive parts of those juices. De Candolle's hypo- 

 thesis is comprehensively described in the 21st Number of the 

 Quarterly Journal of Agriculture. Improving upon the idea of 

 Brugmans, it perceives in this exudation of fecal matter the true 

 theory of the rotation of crops ; that this exuded substance may 

 be regarded in some measure as the excrement of the pre- 

 ceding crop of vegetables, which proves inj urious to succeeding 

 vegetation. The particles which have been deleterious to one 

 tribe cannot but prove injurious to plants of the same kind, and 

 probably to those of some other species, while they furnish nutri- 

 ment to another order of vegetables. Hence, why one kind of 

 corn-crop is injured by immediately succeeding another of the 

 same kind ; hence, why different kinds of crop may with advan- 

 tage succeed one another ; hence, in short, the propriety of a 

 rotation of crops." 



Subsequently, we find that M. Macaire made several experi- 

 ments with chemical re-agents upon plants of Chondrilla murali 



* The query is well put, and merits experimental inquiry. For my own 

 part, although not meaning to impugn the justice of De Candolle's theory, 

 I must confess that I am somewhat sceptical on the subject; and in that I 

 believe many intelligent farmers concur. ~-F, Burke. 



