148 BOARD OF AGRICDLTURE. 



feeding of the plant is done through the leaves. We cannot 

 certainly tell how much goes on through the leaves and liow 

 much through the roots, in highl}^ manured and very rich 

 soil, but experiments have demonstrated that all the carbon 

 of the plant (which is about fifty per cent, of the weight of 

 the dry plant) may come from the atmosphere ; it is not nec- 

 essary that any of it should come from the soil. The seeds 

 of various agricultural plants — Indian corn, oats, barley, etc. 

 — have yielded a larger increase under artificial circumstances, 

 where the roots had no carbon whatever at their disposal, 

 than is ever produced under field culture. It is a well-known 

 fact of agricultural practice, that soils which are nearly des- 

 titute of vegetable matter, and therefore have no considerable 

 source of carbon in them, will produce lai-ge crops. Some 

 very sandy soils, containing but little carbon, may be made to 

 produce heavy crops by irrigation. Crops are also raised on 

 soils free from organic matter, or from sources of carbon, by 

 the aid of fertilizers which themselves furnish nothing of that 

 sort. 



Carbon, then, which makes up half of the weight of the 

 dry plant, is always chiefly supplied by the atmosphere and 

 may be supplied by the atmosphere exclusively. It is not 

 necessary that it should be in the soil. The nitrogen of the 

 plant, which forms indeed a small proportion — two per cent, 

 perhaps, as an average— of the dry plant, is still an impor- 

 tant ingredient, for without it vegetation cannot exist. 



Some crops have the power of gathering nitrogen without 

 any difficulty ; they not only supply themselves with it but 

 they even cause its accumulation in the soil. There are other 

 crops which are dependent upon artificial supplies of nitro- 

 gen, unless the soil be naturally very rich in this element — 

 crops which, if we undertake to raise thsm continuously on the 

 same field, presently begin to show that they lack something, 

 while if we apply nitrogenous compounds as fertilizers, the 

 growth is ensured. We do not know in full detail how plants 

 acquire a sufficient supply of nitrogen from the atmosphere, 

 but we conclude, with great probability, from the results of 

 practice, that different plants draw on the natural supplies of 

 nitrogen in a different way. 



