40 I>K- SCHLEIDEN'S THEORY OF AGRICULTURE. 



The objection that carbon is necessary to supply the carbonic 

 acid requisite for the early stages of vegetable growth, is fully 

 answered by the fact that, if such were the case, it is amply 

 supplied by the atmosphere to the water with which the plant is 

 nourished, and tiiat germinating seeds succeed for a time quite 

 as well in moist quartz sand or cotton as in vegetable soil. 



The only question which remains is, whether carbonic acid 

 is really present in sufficient quantities to supply the demand. 

 This, however, scarcely needs any answer, for by the process of 

 decomposition and vital action the whole of the carbonic acid is 

 returned to the atmosphere, so that it is a simple case of repeated 

 circulation through plants, animals, and atmosphere ; one gene- 

 ration gradually affording the material for another, even were 

 there not other sources which we have no power of estimating. 



But to set the matter beyond all doubt, the following calcula- 

 tion may be made : — 



According to Link, Schwartz, and others, an acre of water 

 meadow produces 4400 lbs. of hay, which, when dry, contains 

 45 . 8 per cent, of carbon. The hay then yields 2000 lbs. of 

 carbon, to which 1000 lbs. may be added for the other portion 

 of the year and for the roots. To produce these 3000 lbs. of 

 carbon, 10,980 lbs. of carbonic acid are requisite, which may be 

 raised to 12,000 lbs., to compensate for the nightly expiration. 

 Now, according to Schubler, an acre of so wretched a grass as 

 Poa annua exhales in 120 days (too low a computation) of 

 active vegetation 6,000,000 lbs. of water. To supply the exi- 

 gencies of the plants then, it is only necessary for it to imbibe 

 3^ grains of carbonic acid with every pound of water. 



2. Nitrogen comes next in order. If there are soluble sub- 

 stances in the soil which could, if necessary, supply the requisite 

 carbon, there are none to furnish the nitrogen. As soon, there- 

 fore, as it was ascertained that plants receive their nitrogen in 

 the form of ammonia, it was generally allowed that organic 

 nitrogenous particles of the soil must first, by decomposition, form 

 ammonia before they can be available for nutrition. The ques- 

 tion, therefore, as to the origin of the nitrogen of plants, assumes 

 quite a different shape from that of carbon. There is no 

 doubt as to the form in which it enters, but whether they depend 

 in greater or less degree on the ammonia contained in the 

 organic matter of the soil, or whether in this respect also they 

 are independent of the organic substances of the soil, is matter 

 of inquiry. 



Now it is clear that the ammonia from the nitrogenous con- 

 stituents of the soil is as available for vegetation as other am- 

 monia, and that our domestic plants do not require a greater 

 supply than in a state of nature. A water meadow which has 



