of the Rotation of Crops. 1 3 



my papers with candour and disinterested feelings, will, I con- 

 ceive, acquit me of undue assumption, or of endeavouring to set 

 up a claim for originality, without just and sufficient reason. 

 That which I borrow I ever wish to avow, as a subject from 

 which I have derived benefit and improvement; but, if I feel 

 confident of having advanced an opinion, or advocated a practice, 

 that, as far as my means of information extend, I conscien- 

 tiously believe to be originally my own, I should be unjust to 

 myself to relinquish that confidence, until, by proof positive, I 

 become convinced that I have laboured under a mistake. 



To quit further preamble, I observe that, at p. 324., we read, 

 " Bragmans stated that a portion of the juices which are ab- 

 sorbed b}' the roots of plants are, after the salutiferous portions 

 have been extracted by the vessels of the plant, again thrown 

 out by exudation from the roots, and deposited in the soil. This 

 idea has been more fully pursued by De Candolle, who sees in 

 it the true theory of the rotation of crops. He thinks it pro- 

 bable that it is the existence of this exuded matter, which may 

 be regarded in some measure as the excrement of the preceding 

 crop of vegetables, that proves injurious to a succeeding vege- 

 tation. . . . The particles which have been deleterious to one 

 tribe of plants cannot but prove injurious to plants of the same 

 kind, and probably to those of some other species, while they 

 furnish nutriment to another order of vegetables. Hence it is 

 why one kind of corn crop is injured by immediately succeeding 

 another of the same kind ; hence why different kinds of crops 

 may with advantage succeed one another ; hence, in short, the 

 propriety of a rotation of crops." 



I do not by any means object to the theory alluded to in this 

 quotation ; far from it, I believe it to be substantially correct : 

 but why is it termed " De Candolle's theory ?" That learned 

 professor has advocated the facts stated : so, it appears, did Pro- 

 fessor Brugmans. I was not, indeed, aware that that learned 

 German had written at all on the subject ; nor do I now know 

 in what work his opinions are to be found ; but it appears that 

 he preceded M. de Candolle at the least. Dr. Lindley, also, it 

 can be proved, published a hypothesis by no means at variance 

 with the theory under consideration. In his Outlines of the First 

 Principles of Horticulture (No. $2 — 56.) we read, " Spongioles 

 secrete excrementitious matter, which is unsuitable to the same 

 species afterwards as food ; for poisonous substances are as fatal 

 to the species that secrete them as to any other species. ... But 

 to other species the excrementitious matter is either not unsuit- 

 able or not deleterious. . . . Hence, soil may be rendered impure 

 (or, as we inaccurately say, worn out) for one species, which will 

 not be impure for others. . . . This is the true theory of the 

 rotation of crops." 



