74 OF THE INORGANIC CONSTITUENTS OF PLANTS. 



the same quantity of fir-wood only 83, of lime-wood 500, of rye 

 440, and of the herb of the potatoe plant 1500 parts.* 



Firs and pines find a sufficient quantity of alkalies in granitic 

 and barren sandy soils in which oaks will not grow ; and wheat 

 thrives in soils favorable for the lime-tree, because the bases 

 necessary to bring it to complete maturity exist there in suffi- 

 cient quantity. The accuracy of these conclusions, so highly 

 important to agriculture and to the cultivation of forests, can be 

 proved by the most evident facts. 



All kinds of grasses, and the Equisetaccaz, for example, con- 

 tain in the outer parts of their leaves and stalk, a large quantity 

 of silicic acid and potash in the form of acid silicate of potash . The 

 proportion of this salt does not vary perceptibly in the soil of 

 corn-fields, if it be again conveyed to them as manure in the form 

 of putrefying straw. But this is not the case in a meadow, and 

 hence we never find a luxuriant crop of grass f on sandy and cal- 

 careous soils containing little potash, evidently because one of the 

 cor.stituents indispensable to the growth of the plants is wanting. 

 Soils formed from basalt, grauwacke, and porphyry, are, caderis 

 paribus, the best for meadow-land, on account of the large quan- 

 tity of potash they contain. The potash abstracted by the 

 plants is restored during the annual irrigation. The amount of 

 alkalies contained in the soil itself is very great in com- 

 parison with the quantity removed by plants, although not 

 inexhaustible. 



A harvest of grain is obtained every thirty or forty years 

 from the soil of the Luneburg heath by strewing it with the 

 ashes of the heath-plants (Erica vulgaris) growing upon it. 

 These plants, during the long period just mentioned, collect the 

 potash and soda contained in the soil and conveyed to them by 

 rain-water ; and it is by means of these alkalies that oats, barley, 

 and rye, to which they are indispensable, are enabled to grow on 

 this sandy heath. 



* Berthier, Annales de Chimie et de Physique, t. xxx., p. 248. 



f It would be of importance to examine what alkalies are contained in 



the ashes of the sea-shore plants which grow in the humid hollows of 



# downs, and especially those of the millet-grass If potash is not found in 



them, it must certainly be replaced by soda, as in the Salsota, or by lime, 



m in the Plumbaginea. 



