CONSTITUENTS OF PLANTS. 105 



to the cultivation of forests, can be proved by the 

 most evident facts. 



All kinds of grasses, the Equisetacece, for example, 

 contain 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, because it is again conveyed to them 

 as manure in the form of putrifying straw. But 

 this is not the case in a meadow, and hence we 

 never find a luxuriant crop of grass* on sandy and 

 calcareous soils which contain little potash, evi- 

 dently because one of the constituents indispensable 

 to the growth of the plants is wanting. Soils formed 

 from basalt, grauwacke, and porphyry are, caeteris 

 paribus, the best for meadow land, on account of 

 the quantity of potash which enters into their com- 

 position. The potash abstracted by the plants is re- 

 stored during the annual irrigation-^. That con- 



* 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 in those of the millet-grass (Hartig). 

 If potash is not found in them it must certainly be replaced by soda as 

 in the salsola, or by lime as in the Plumbacfinece. 



f A very high value is attached in Germany to the cultivation of 

 grass as winter provision for cattle, and the greatest care is used in 

 order to obtain the greatest possible quantity. In the vicinity of Liegen 

 (a town in Nassau), from three to five perfect crops are obtained from 

 one meadow, and this is effected by covering the fields with river- water, 

 which is conducted over the meadow in spring by numerous small 

 canals. This is found to be of such advantage, that supposing a meadow 

 not so treated to yield 1000 Ibs. of hay, then from one thus watered 

 4'5000 Ibs. are produced. In respect to the cultivation of meadows, the 

 country around Liegen is considered to be the best in all Germany. 



