76 OF THE INORGANIC CONSTITUENTS OF PLANTS. 



cut down. The bark and foliage of oaks, for example, contain 

 from 6 to 9 per cent, of alkalies, the needles of firs and pines, 8 

 per celA. 



With every 2650 lbs. of firwood yearly removed from an acre 

 of forest, only 7 or 8 lbs. of alkalies are abstracted from the soil, 

 calculating the ashes at 0.83 per cent. The leaves, however, 

 cover the soil, and being very rich in alkalies, in comparison 

 with the wood, retain those alkalies on the surface, which would 

 otherwise so easily penetrate with the rain through the sandy 

 soil. By their decay an abundant provision of alkalies is sup- 

 plied to the roots of the trees, and a fresh supply is rendered 

 unnecessary. 



The ashes of the tobacco plant, of the vine, of peas, and of 

 clover, contain a large quantity of lime. Such plants do not 

 flourish on soils devoid of lime. By the addition of salts of lime 

 to such soils, they become fitted for the growth of these plants ; 

 for we have every reason to believe that their development es- 

 sentially depends upon the presence of lime. The presence of 

 magnesia is equally essential, there being many plants, such as 

 the different varieties of beet and potatoes, from which it is never 

 absent. 



The supposition that alkalies, metallic oxides, or inorganic mat- 

 ter in general, are produced by plants, is entirely refuted by 

 these well-authenticated facts. 



It is thought very remarkable, that the plants of the grass 

 tribe, fitted for the food of man, follow him like the domestic 

 animals. But saline plants seek the sea-shore or saline springs, 

 and the Chenopodium the dunghill, from similar causes. Saline 

 plants require common salt, and the plants growing only on dung- 

 hills need ammonia and nitrates, and they are attracted to places 

 where these can be found, just as the dung-fly is to animal ex- 

 crements. So likewise none of our corn plants can bear perfect 

 seeds, that is, seeds yielding flour, without a large supply of 

 phosphate of magnesia and ammonia, substances which they re- 

 quire for their maturity. And hence, these plants grow only in 

 a soil where these three constituents are found combined, and no 

 soil is richer in them than those where men and animals dwell 

 together ; where the urine and excrements of these are found 



