SELECTION OF SEED; FARM CROPS. 131 



summer, before the conditions are favorable for tbe rapid 

 change of organic nitrogen into nitrates — are more bene- 

 fited by a direct application of nitrates than corn, which, 

 besides being a cultivated crop, makes its greatest growth 

 in late summer, when the decay and consequent nitrifica- 

 tion of the organic matter is most active. 



Soil Exhaustion. — The cereals are exhaustive crops, 

 because the food constituents gathered are largely trans- 

 ferred from the stem and leaf, and concentrated in the 

 grain, which is sold from the farm. 



Forage Crops ; Grasses. — Nearly all varieties of 

 grasses are perennial, though the length of life depends 

 upon the method of cropping and character of soil. 

 Where the grass is allowed to seed, it dies quicker than 

 when it is pastured or cut before maturity, because the 

 depth of root is measured to some extent by the length 

 of top. On poor, dry soils, also, the life is shorter than 

 upon moist soils of fair fertility. 



Methods of Growth. — The grasses send out their 

 fibrous roots into the surface soil in the same manner 

 as the cereals, though they differ from the cereals in 

 forming each year a set of buds just below the surface 

 of the ground, which become active in the late summer, 

 and develop new shoots and roots ; as this budding 

 ceases, the plants die. Those which produce the great- 

 est number of branches, and continue the process for a 

 succession of years, are the most valuable permanent 

 grasses ; those that form their branches in compact tufts 

 have less hold upon the ground, and are more liable to 

 be uprooted by animals, and to be destroyed by unfavor- 

 able conditions of soil and season, than those which pos- 



