DR SCHLEIDEN'S THEORY OF AGKICULTUEE. 43 



"We have still to consider those inorganic substances which 

 remain in the ashes when a plant is burnt. 



It has been already seen that the inorganic or mineral con- 

 stituents of the soil are of the most importance not only for plants 

 in general, but for plants of husbandry. Tiiis is no new theory ; 

 it was broached by De Saussure in the last century ; and even 

 before Liebig reproduced it in a more perfect form, it had been 

 acknowledged by Thaer and some other genial spirits. Notwith- 

 standing all the great difficulties \\hich are involved in the study 

 of the inorganic constituents of plants, their importance is un- 

 questionable ; and when we compare the analyses of their ashes, 

 conducted on tlie same uniform plan, the result is incontestable 

 that different plants are distinguished by the quantity and quality 

 of their inorganic contents. Unfortunately such analyses have 

 been confined principally to plants under cultivation. But with 

 differences of outward form and modifications of cliemical action 

 there must be great differences also of inorganic contents. We 

 cannot indeed at present follow the intimate connexion between 

 the process of vegetation and the inorganic constituents, yet the 

 certainty of this connexion is beyond all doubt. Take what 

 plant we may, we always find that witli a different content in 

 organic constituents there is a difference in the quantity of 

 inorganic matters. We may refer to Boussingault's table of 

 comparison of the nitrogen and phosphoric acid in plants : from 

 this it appears that the proi)ortion of phosphoric acid to nitrogen 

 is tolerably constant ; yet the phosphoric acid is in no general 

 necessary proportion to tlie nitrogen. It is very probable there- 

 fore tliat pliosphoric acid does not contribute directly to the 

 formation of the nitrogenous parts, for albumen, gluten, and 

 legumin contain nearly the same quantity of phosphorus, viz., 

 about 0-3 per cent., although the proportion of phosphoric acid 

 to nitrogen in the plants which afford gluten, as wheat, maize, 

 and oats, is as 1 : 2*9 ; in the albuminous i)lants (as hay, potatoes, 

 mangel wurzel, stubble turnips, and Jerusalem artichokes), as 

 1"35 ; and in those which contain legumin (as clover, beans, 

 peas, and kidney beans), as 1 : 4*6. 



It is self-evident tiiat the inorganic constituents of plants are 

 received from the soil in solution with water. It remains only to 

 inquire what inorganic constituents are most important for do- 

 mestic plants. They require indeed in kind the same as wild 

 plants, but the question as to quantity is verj- different. They 

 yield in general nearly twice as mucli of inorganic ashes. 



Flint is mostly found in the walls of the cells in which it is 

 deposited, and whicli it helps to strengthen ; and the same may be 

 said of a portion of the lime, wiiich enters as a pectate into an 

 insoluble combination with the gelatinous component of the cell 



