250 DR. DAUBENY ON THE ROTATION OF CROPS, ETC. 



which contained four grains of phosphate of lime in 1000 grains, whereas ours scarcely 

 exceeded one-fourth of a grain in the same quantity ; and if the former be regarded 

 as an exceptional case, I might refer to Sprengel, who states, that the per-centage 

 of phosphoric acid in the soils he analysed varied from 0*024 to 0'367 ; and of the 

 subsoil from about 0007 to 0*2. 



I detected many years ago phosphate of lime in several secondary limestones 

 chiefly from the oolitic formation, and Mr. Schweitzer of Brighton has determined 

 the proportion of that ingredient in the chalk near Brighton, to be not less than one 

 grain in the 1000. We need not therefore resort to South America for bones, if 

 means could be found for extracting this ingredient economically from the rocks of 

 our own country. 



3rdly. These facts place in rather a new light, although one, it is conceived, not 

 less striking than before, the importance of taking care of the various excrementitious 

 matters at our disposal, whether proceeding from animal or from vegetable sources. 



Such substances indeed contain the products, which nature has, with so large a 

 consumption of time, and by such a number of complicated operations, elaborated 

 from the raw material contained in the soil, and has at length brought into the con- 

 dition, in which they are most soluble, and therefore best fitted to be assimilated by 

 the organs of plants. 



To waste them, is therefore to undo, what has been expressly prepared for our use 

 by a beautiful system of contrivances, and to place ourselves under the necessity of 

 performing, by an expenditure of our own labour and capital, those very processes, 

 which nature had already accomplished for us, without cost, by the aid of those 

 animate or inanimate agents which she has at her disposal. 



4thly. The analyses above reported may suggest caution as to the inferences which 

 some might be disposed to deduce from certain researches lately announced, with re- 

 spect to the power which a plant possesses of substituting one alkali, or one earth, 

 for another, in the processes of vegetation. 



This substitution indeed, however brought about, is a fact which hardly admits of 

 being questioned, supported as it is by the testimony of men so eminent as Saussure 

 and as Liebig, and indeed many of the analyses detailed in this paper might be ap- 

 pealed to in corroboration of its truth. 



Thus we find, that whilst the amount of bases agreed pretty nearly in the three 

 crops of the same plant which had been analysed, the proportions between them 

 often varied considerably. This is particularly seen in the case of the lime and mag- 

 nesia, the deficiency in one of these earths being often made up by an excess in the 

 other. 



In like manner a deficiency of potass is found to be compensated by an increased 

 amount of soda, and the same remark seems to apply to the acids. 



Still we have not as yet sufficient data for determining to what extent this ex- 

 change of the usual ingredient for another can take place ; whether indeed the same 



