* -Royal Society, SAS 



ing the theory of DcCandolle, in which the deterioration experienced 

 by most crops on tlieir repetition was attributed to the deleterious 

 influence of their root-excretions. For this purpose he set apart, 

 ten years ago, a number of plots of ground in the Botanic Garden 

 at Oxford, uniform as to quality and richness, one-half of which 

 was planted each year, up to the present time, with the same species 

 of crop, and the other half with the same kinds, succeeding each 

 other in such a manner that no one plot should receive the same 

 crop twice during the time of the continuance of the experiments, 

 or at least not within a short period of one another. The difference 

 iil the produce obtained in the two crops, under these circumstances, 

 would, the author conceived, represent the degree of influence 

 ascribable to the root-excretions. 



The results obtained during the first few years from these experi- 

 ments, as well as from the researches which had, in the mean time, 

 been communicated to the world by M. Braconnot and others on 

 the same subject, led him in a great measure to abandon this theory, 

 and to seek for some other mode of explaining the falling off" of crops 

 on repetition. In order to clear up the matter, he determined to 

 ascertain, for a series of years, not only the amount of crop which 

 would be obtained from each of the plants tried under these two 

 systems, but also the quantity of inorganic matters extracted in each 

 case from the soil, and the chemical constitution of the latter, which 

 had furnished these ingredients. The chemical examination of the 

 crops, however, on account of the labour it involved, was confined 

 to six out of the number of the plants cultivated ; and of these, three 

 samples were analysed, the first being the permanent one, viz. that 

 cultivated for nine or ten successive years in the same plot of 

 ground ; the second, the shifting one, obtained from a plot which 

 had borne different crops in the preceding years ; the third, the 

 standard, derived from a sample of average quality, grown under 

 natural circumstances, either in the Botanic Garden itself, or in the 

 neighbourhood of Oxford. These analyses were performed by Mr. 

 Way, formerly assistant to Professor Graham, of University Col- 

 lege, London, and now attached to the Agricultural College near 

 Cirencester. 



The examination of the soils was carried on in two ways; the 

 first, with the view of estimating the entire amount of their avail- 

 able ingredients ; and the second, with that of ascertaining the quan- 

 tity in a state to be taken up at once by plants, the available ingre- 

 dients being those which are soluble in muriatic acid; the active 

 ones, those which are taken up by water impregnated with carbonic 

 acid gas. This portion of the investigation was conducted in part 

 by the author, and in part by Mr. Way, and has reference to three 

 subjects ; first, to the amount of produce obtained from the deficient 

 crops ; secondly, to their chemical constitution ; and thirdly, to the 

 nature of the soil in which the crops were severally grown. 



The plants experimented upon were spurge, potatoes, barley, tur- 

 nips, hemp, flax, beans, tobacco, poppies, buckwheat, clover, oats, 

 beet, mint, endive, and parsley. The only crop which seemed to 



