OF SOIL AND MANUEE. 339 



mon salt ; or by their power of absorbing moisture 

 from the atmosphere, as salt and the muriate of lime, 



(lAebig, op. cit. p. 145.) "A soil which has been exposed for cen- 

 turies to all the influences which effect the disintegration of rocks, 

 but from which the alkalies have not been removed, will be able to 

 afford the means of nourishment to those vegetables which require 

 alkalies for their growth during many years ; but it must gradually 

 become exhausted, unless those alkalies which have been removed 

 are again replaced : a period therefore will arrive when it will be 

 necessary to expose it, from time to time, to a further disintegration, 

 in order to obtain a new supply of soluble alkalies. For small as is 

 the quantity of alkali which plants require, it is nevertheless quite 

 indispensable for their perfect developement. But when one or more 

 years have elapsed without any alkalies having been extracted from 

 the soil, a new harvest may be expected. The first colonists of Vir- 

 ginia found a country, the soil of which was similar to that mention- 

 ed above ; harvests of Wheat and Tobacco were obtained for a cen- 

 tury from one and the same field, without the aid of manure ; but 

 now whole districts are converted into unfruitful pasture land, which 

 without manure produces neither Wheat nor Tobacco. From every 

 acre of this land there were removed, in the space of 100 years, 1200 

 lbs. of alkalies in leaves, grain, and straw ; it became unfruitful, 

 therefore, because it was deprived of every pni'tiele of alkali which 

 had been reduced to a soluble state, and because that which was 

 rendered soluble again in the space of one year was not sufiicient to 

 satisfy the demands of the plants. . . . It »s the greatest possible 

 mistake to suppose that the temporary diminution of fertility in a 

 soil is owing to the loss of humus [vegetable mould] ; it is the mere 

 consequence of the exhaustion of the alkalies." (Op. cit. p. 148.) 

 This proposition is very perfectly made out by this distinguished 

 organic chemist ; and the true theory of the operation of manure, 

 of the interchange of crops, Ac., is thence readily and satisfactorily 

 deduced. The limits of a note will not allow us to enter farther into 

 the consideration ot this subject, so important to agriculture and 

 horticulture ; which is the less necessary, now that an American edi- 

 tion of the work ft-om which these observations are drawn has been 

 announced. G.] 



