FALLOW-CROPS. 15/ 



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 appropriated by plants. 



Now, it is evident, that the careful tilling of fallow 

 land must increase and accelerate this disintegra- 

 tion. For the purpose of agriculture, it is quite 

 indifferent, 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 Vicia faba, for example, contains no 

 free alkalies, and not one per cent, of the phos- 

 phates of lime and magnesia (Eirikof). The bean 

 of the Phaseolus Vulgaris contains only traces of 

 salts (Braconnot). The stem of the Medicago sativa 

 contains only 0*83 per cent., that of the 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 

 those which are termed fallow-crops, and the cause 

 wherefore they do not exercise any injurious influ- 

 ence on corn which is cultivated immediately after 



* 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. 



