NECESSITY OF CERTAIN CONDITIONS FOR NUTRITION. 121 



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 seashore or saline springs, 

 and the Chenopodiu^n 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 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 require for their 

 maturity. And hence, these plants grow only in a 

 soil where these three constituents are found com- 

 bined, 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 seeds cannot attain maturity un- 

 less supplied with the constituents of those matters. 



When we find sea-plants near our salt-works, 

 several hundred miles distant from the sea, we know 

 that their seeds have been carried there in a very 

 natural manner, namely, by wind or birds, which 

 have spread them over the whole surface of the 

 earth, although they grow only in those places in 

 which they find the conditions essential to their life. 



Numerous small fish, of not more than two inches 

 in length ( Gasterosteus aculeatus), are found in the 

 salt-pans of the graduating house at Nidda (a vil- 

 lage in Hesse Darmstadt). No living animal is found 

 in the salt-pans of Neuheim, situated about 18 miles 

 from Nidda ; but the water there contains so much 

 carbonic acid and lime, that the walls of the gradu- 

 ating house are covered with stalactites. Hence 

 11 



