1834.] Scientific Intelligence. 149 



work will be maintained through every department of labour. To a steady ad- 

 herence to this practice is justly ascribed all the improvements on land which have 

 attracted the admiration of every lover of this country : to it is properly attributed 

 the regular apportionment of an invariable extent of land, which is annually devot- 

 ed to the growth of culmiferous crops ; and which regularly checks, as far as 

 human means can, injurious fluctuation in the supply of the first necessary of life : 

 and to it is accurately imputed the supply of the immense numbers of high-fed 

 live-stock which daily grace our markets. 



To the intelligent agriculturist it is delightful to learn that the discoveries of 

 science tend more and more to develop those principles which his practice illus- 

 trates. That practice has hitherto kept " the even tenor of its way," by the guid- 

 ance of unerring experience, amid the contempt of scientific reproach. It now 

 receives its justification in the confession of scientific error. 



Various reasonings have hitherto been employed by men of science to account 

 for the necessity of a rotation of crops. It has been thought sufficient to explain 

 all the phenomena to state, that different plants absorb different juices from the 

 same soil, and, therefore, though the ground may be exhausted by one class of 

 vegetables, it may be rich enough for another. But it is well known to botanical 

 physiologists, that plants absorb all the soluble substances which the soil contains 

 whether injurious to their growth or not. It has also been stated as an explana- 

 tion, that the roots of different plants, being of different lengths, extend into dif- 

 ferent layers of the soil, and thus derive from it adequate nourishment. But the 

 roots of all plants must be in the same stratum at the period of germination, and 

 it is besides probable that all the arable part of the soil is homogeneous. It is 

 known that plants of the same family, such as clover and lucerne, do not prosper 

 in succession, although their roots are of different lengths. These theories are 

 therefore not satisfactory. 



Brugmans stated that a portion of the juices which are absorbed by 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 probable, 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 vegetation. 

 He has compared it to an attempt to feed animals upon their excrements. The 

 particles which have been deleterious to one tribe of plants, cannot but prove in- 

 jurious to plants of the same kind, and probably to those of some other species, 

 while they furnish nutriment to another order of vegetables. Hence why one 

 kind of corn crop is insured by immediately succeeding another of the same kind ; 

 hence why different kinds of crop may with advantage succeed one another ; hence 

 in short, the propriety of a rotation of crops. 



To subject these theoretic views to the test of experiment, M.I. Macaire has made 

 many experiments to prove that vegetables exude matter from the roots, and which 

 are related by him in a memoir inserted in the Transactions of the Soctitt de Phy- 

 sique et d'Histoire Naturelle of Geneva*. After various attempts to raise plants 

 in pure siliceous sand, pounded glass, washed sponge, white linen, he decided 

 upon pure rain-water. After cleansing and washing the roots thoroughly, he 

 placed them in vials with a certain quantity of pure water. After they had put 

 forth leaves, expanded their flowers, and flourished for some time, he ascertained, 

 by the evaporation of the water, and the use of chemical re -agents, that the water 

 » See Edinburgh New Philosophical Journal, No. xxviii. p, 215. 



