CONSTITUENTS OF PLANTS. 109 



The moss, however, which covers the ground, and 

 of which the ashes are known to contain so much 

 alkali, continues uninterrupted in its growth, and 

 retains that potash on the surface, which would 

 otherwise so easily penetrate with the rain through 

 the sandy soil. By its decay, an abundant pro- 

 vision of alkalies is supplied to the roots of the 

 trees, and a fresh supply is rendered unnecessary. 



The supposition of alkalies, metallic oxides, or in- 

 organic matter in general, being produced by plants, 

 is entirely refuted by these well-authenticated facts. 



It is thought very remarkable, that those plants 

 of the grass tribe, the seeds of which furnish food 

 for 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, which grow only on dunghills, 

 need ammonia and nitrates, and they are attracted 

 whither these can be found, just as the dung-fly 

 is to animal excrements. 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 require 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 corn -plants appear, because their 



