118 FOOD OF PLANTS. 



much greater variation in the ashes, which consist mostly of 

 potash, silex, lime, sulphur, 2^hosphorus, and some other elements 

 in minute quantities. 



2X2* The first four elements are called organic elements, or 

 • organogens ; the materials of the ashes, inorganic eleynents. The 

 most abundant element is carbon, and no organic product exists 

 without it, although either of the others may be absent. 



213. The plant derives its carbon from carbonic acid, COg. 

 It cannot take up carbon in an uncombined state, as it is solid, 

 and it can obtain it from no other compound of carbon, as no 

 other exists in sufficient quantities. The carbonic acid in tl;e 

 air, the result of respiration of animals, the combustion of wood 

 and coal, and the decay of carbonaceous substances, and that 

 contained in the soil from the action of manure, affords the plant 

 its carbon. It is chiefly derived from the air. Numerous facts 

 prove this position. Originally, before there was any vegeta- 

 tion, there could have been carbonic acid nowhere else. Plants 

 grow in the air and deposit carbon. The growth of plants in- 

 creases the carbonaceous matter in the soil w^here they grow. 

 Plants will grow and increase in carbon in distilled water. 

 These well-known facts prove that carbonic acid in the atmos- 

 phere supplies most of the carbon to plants. 



214. The oxygen and hydrogen in plants are principally de- 

 rived from water, OH ; hydrogen, perhaps, partly from ammonia. 



215. Nitrogen is obtained by the plant mostly by the decom- 

 position of Ammonia, NH3. Ammonia is generated wherever 

 organic substances are decaying, especially animal substances. 

 The ammonia is dissolved in water, and absorbed by porous 

 substances in the soil, and from either condition is furnished to 

 the roots of the plants. During thunder-storms small quantities 

 of nitric acid, NOj, are produced, which is brought down by the 

 rains, and in a very diluted state furnishes food for the plant in 

 the form of N and O. Volcanoes and springs probably throw 

 out immense quantities of the gases that afitord food to plants, 

 especially Carbonic Acid and Ammonia. 



216. Although the above four elements are the organic ele- 

 ments of plants, yet, for the perfection of any plant, except of the' 

 very lowest character, inorganic elements are essentially neces- 

 sary. Sulphur and Phosphorus are essential to the production 



212. What are the first four elements called? Elements in the ashes? 

 VVliich element is universal ?— 213. Wlience does the plant derive its 

 carbon? Whence comes the carbonic acid ? What facts prove this posi- 

 tion ? -214. Whence oxygen and hydrogen ? — 215. Whence the nitrogen ? 

 —216. What other elements are necessary? For what are sulphur and 

 phosphorus essential ? 



