76 FOOD OF THE VEGETATING PLANT. CHAP. IT. 



the same manure or mould, will produce equal 

 quantities of ashes. But this supposes manures to 

 have the same action upon all soils, which is surely 

 not the fact : and if there be any manure that acts 

 on a calcareous soil, without acting at all on a grani- 

 tic soil, then the quantity of ashes will be altered 

 in the former case, from that very circumstance; 

 because the plant is now nourished not only by the 

 manure that was committed to the soil, but from 

 the original soil itself, in its state of combination 

 \vith the manure. 



Aborbed The earths, then, that are contained in vegetables 

 lion? U a ** e derived chiefly from the soil : but in what 

 peculiar state of combination do they enter the 

 vessels of the plant ? The state most likely to faci- 

 litate their absorption is that of their solution in 

 water, in which all the earths hitherto found in 

 plants are known to be in a slight degree soluble. 



Lime is soluble in water with the aid of a little 

 carbonic acid, in the proportion of about -5-1-5- part 

 of its weight ; but it is also soluble even without 

 the aid of the acid,* and the solution is known by 

 the name of lime-water. Clay is soluble in water 

 by means of the mineral acids ; and also, though 

 very sparingly, in pure water, from which even the 

 filtre cannot abstract it.-f- Silica is soluble in water 

 by means of carbonate of potass, as is evident from 

 Black's analysis of the waters of Geyser in Iceland. 

 It is soluble also in pure water according to the 

 * Scneb. Phys. Veg. vol. iii. p. 17, f Ibid. 



