FALLOW-CROPS. 159 



wheat, from the time of its flowering, restores a part 

 of its organic constituents to the soil, although the 

 phosphate of magnesia remains in the seeds. 



The fallow-time, as we have already shown, is that 

 period of culture during which land is exposed to a 

 progressive disintegration by means of the influence 

 of the atmosphere, for the purpose of rendering a 

 certain quantity of alkalies capable of being appro- 

 priated by plants. 



Now, it is evident, that the careful tilling of fal- 

 low-land must increase and accelerate this disinte- 

 gration. For the purpose of agriculture, it is quite 

 indiffierent, whether the land is covered with weeds, 

 or with a plant which does not abstract the potash 

 inclosed in it. Now many plants in the family of 

 the leguminosce are remarkable on account of the 

 small quantity of alkalies or salts in general which 

 they contain; the Windsor bean ( Fzcm Faba), fov 

 example, contains no free alkalies, and not one per 

 cent, of the phosphates of lime and magnesia. 

 (Einhof.) The bean of the kidney-bean •(P/^a5eo/?^5 

 vulgaris) contains only traces of salts. (Braconnot.) 

 The stem of Lucern [Medicago sativa) contains only 

 0*83 per cent., that of the Lentil {^Ervum Lens) 

 only 0*57 of phosphate of lime with albumen. 

 (Crome.) Buck-wheat dried in the sun yields only 

 0-681 per cent, of ashes, of which 0*09 parts are 

 soluble salts. (Zenneck.)* These plants belong to 



* The small quantity of phosphates which the seeds of the lentils, 

 beans, and peas contain, must be the cause of their small value as 

 articles of nourishment, since they surpass all other vegetable food in 

 the quantity of nitrogen which enters into their composition. But as 

 the component parts of the bones (phosphate of lime and magnesia) 

 are absent, they satisfy the appetite without increasing the strength. 

 The following is an analysis of lentils (Playfair). 6-092 grammes lost 

 0-972 grammes of water at 212°. 0.566 grammes, burned with oxide 

 of copper, gave 0*910 grammes carbonic acid and 336 grammes of 

 water. The lentils on combustion with oxide of copper, yielded a gas, 

 in which the proportion of the nitrogen to the carbonic acid was 

 asl: 16. 



Carbon 44 45 



Hydrogen 6-59 



Nitrogen 642 



Water 15 95 



