[391] SCIENTIFIC MANUAL. 105 



soil, but return, also, vast quantities of those substances 

 taken from the atmosphere to ameliorate the mechanical 

 condition of the soil, and serve as absorbents of moisture 

 and fertilizing gases from the air. 



A certain class of plants, known as legumes, embracing 

 the clovers, lucern, peas, beans, and other pod-bearing 

 plants, are especially beneficial as soil fertilizers. 



Their long tap-roots penetrate deep into the subsoil, 

 from which they assimilate mineral food, which, after being 

 used in building up the leaves and stems of the plants, is 

 deposited, at their death, on the surface soil, to be used by 

 future crops. Besides this power of deep penetration, this 

 class of plants has greater capacity for decomposing and 

 appropriating mineral matter and nitrogen from the soi* 

 than other plants, and are supposed to have a peculiar pow- 

 er of absorbing ammonia from the atmosphere. By refer- 

 ence to the tables of analyses of plants, in the appendix of 

 this work, it will be seen that the legumes are especially 

 rich in nitrogen and the important mineral elements, pot- 

 ash, phosphoric acid, lime, etc. The large quantity of 

 nitrogen which they contain, facilitates their decay, and 

 thus hastens the restoration of their mineral elements to 

 the soil. 



The peculiar benefits derived from decayed vegetable 

 matter, have already been given in detail in this work. 



By the application of mineral fertilizers to the legumi- 

 nous plants, their growth is largely increased, and thus 

 their fertilizing capacity improved. 



It is a fact well known to practical farmers, that even 

 when the crop of clover or pea vines is removed from the 

 land, its producing capacity for the grasses or cereals is 

 materially increased. 



The improvement is still greater when the crop is turned 

 under, or allowed to decay upon the land. 



Where there are beds of muck, rich in vegetable matter, 

 it may be banked, in position, during dry spells in summer, 



