230 CONSERVATIVE ORGANS. [LECT. V. 



quantities, added together, nearly equal the ori- 

 ginal quantity of the specimen, the analysis may 

 be considered as accurate. Many little niceties of 

 manipulation are necessary to be attended to; 

 but, for these and other particulars requisite to be 

 examined when the analysis is required to be very 

 accurate, I must refer you to Sir H. Davy's ad- 

 mirable work on Agricultural Chymistry, which is 

 the source of much of the information contained 

 in this Lecture. Let us now examine in what way 

 the components of a soil affect plants ; and which 

 of these are taken into the vegetable system. 



The principal matter, undoubtedly, that plants 

 take up from the soil is water; and from the results 

 of several experiments in rearing plants in pure 

 water, this fluid has been by many supposed to be 

 the only food of plants. But when these experi- 

 ments were repeated with greater care, and the 

 water employed to moisten the pure sand in 

 which the seeds were planted was distilled, the 

 plants thus raised were found not to have gained 

 any augmentation of vegetable matter ; and sel- 

 dom or never perfected their seeds, although they 

 flowered. In some cases, however, a small ad- 

 dition of vegetable matter had been gained. We 

 have already ascertained that the elements of ve- 

 getable matter are carbon, hydrogen, and oxygen ; 

 and as we know also that water is composed of 

 hydrogen and oxygen, we can easily believe that 



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