HORTICIjLTURAL SOriETY OF LONDON. 



341 



combined with lime alone, but in the former partly in combina- 

 tion with soda. 



It is easy to ascertain with great accuracy the quantity of 

 sulphuric acid present in a plant, as the tests for that substance 

 are easily used, and the acid is not liable to be soon decomposed 

 by any change which may take place in the organic matter of the 

 plant. In the case of some acids however, such as nitric acid, 

 the question is one of more difficulty, because not only are the 

 tests for it less certain, but the acid itself is rather liable to un- 

 dergo decomposition and change in the organs of the plant 3 

 hence experiments on this acid are less satisfactory than most 

 others. The subject is however so important, that new experi- 

 ments are required to make the matter certain and intelligible. 

 I believe that in many cases, very beneficial effects were pro- 

 duced on peas, beans, lettuces, and even on young trees, by nitrate 

 of potash or soda, the salt being absorbed from the soil in an 

 unaltered state, and producing those marked effects which have 

 been so frequently observed ; without having been decomposed. 

 I did not at all times obtain this result, for some times no trace of 

 nitrate could be detected in the plants which had been watered 

 with it; It is hardly probable that under ordinary circumstances, 

 these nitrates could be decomposed by any matters present in the 

 soil, for the tendency of most soils is to form, rather than decom- 

 pose them, and it is well known that some plants require and 

 absorb nitrates from the soil, such as lettuces, tobacco, sun- 

 flowers, &c. the leaves of which contain so large a quantity of 

 nitrates, that when dried they burn like Amadou or tinder. 

 Plants of this kind absorb nitrates artificially applied to the 

 ground and are immediately benefited by its application, though 

 the salt is absorbed whole, and not decomposed. 



Though in general I abstain from making any reference to the 

 experiments on soils, on which I have been for some time past 

 engaged, I may perhaps say a few words respecting the nature of 

 the serpentine soils of Cornwall. The results of the investiga- 

 tion instituted by Sir Charles Lemon in the composition of the 

 soils in some of the serpentine districts of Cornwall, seemed to 

 me so very strange and unexpected, and so totally opposed to the 

 commonly received theories of the formation of soils, that I was 

 glad to avail myself of an opportunity of examining a portion of 

 the soil. It was stated that the soil which rested on the serpen- 

 tine was destitute of magnesia, though the rock Uelow contained 

 nearly thirty per cent. It may, perhaps, seem unnecessary to 

 say that my experiments agreed in the main with those of the 

 Chemists who had previously examined it, but I think it is worth 

 while to add, that although I did find a remarkably small quait- 

 No. XIX. B 



