164 BIOLOGY OF PLANTS. 



Humic acid is composed of hydrogen, oxygen and carbon. 

 Crenic acid is composed, according to Hermann, of forty- 

 two parts by weight of carbon, sixteen of hydrogen, four- 

 teen of nitrogen, forty-eight of oxygen. Apocrenic acid is 

 composed of eighty-four parts of carbon, fourteen of hydro- 

 gen, forty-two of nitrogen, and twenty-four of oxygen. These 

 latter acids are soluble in water, even when combined with 

 bases, and contain a quantity of nitrogen, which must enter 

 the organs of plants. We have then, only to suppose similar 

 organic transformations, in order that their nitrogen may be 

 assimilated to the vegetable organs. As a part of the carbon 

 is derived from the soil, so a part, at least, of the nitrogen 

 may be derived from the same source. 



The influence of crenate of lime (which is sometimes 

 found in the sub-soil) upon clover, favors the idea, that it 

 furnishes a quantity of the nitrogen to seeds, fruits, and other 

 parts of vegetables ; for it is found that clover contains nearly 

 double the quantity of nitrogen \vhich is found in many other 

 grasses. 



4. Nitric acid. The putrefaction of animal bodies, yields 

 large quantities of nitric acid, especially by the fermentation 

 of manures. This acid combines with potash, soda and am- 

 monia, to form salts, which are found, more or less abundant, 

 in all fermented manures. The salts are soluble in water, and 

 must enter the vegetable organs. The acid is composed of 

 fourteen parts of nitrogen and forty of oxygen. Here, then, 

 is another source of the nitrogen of plants. That plants de- 

 rive a part, at least, of their nitrogen from this source, is 

 proved by the most incontestable facts. 



Daubeny has shown, that nitrate of soda, placed upon lands 

 sown with wheat, increased the gluten of the wheat 4.25 per 

 cent., and the albumcnl 0.75 per cent. The gluten and 

 albumen contain great quantities of nitrogen, and will be 

 abundant in the seed, in proportion to the proper sup})ly of 

 matters from which they may obtain it. Whence did they 



