70 BOTANY OF CROP PLANTS 



rice cut grass (Homalocenchrus) are feeble climbers or support 

 themselves by means of numerous hooked prickles on their 

 leaves. 



Many of our common pasture and meadow grasses, and 

 all the cereals, complete their life period in one season. Such 

 plants are said to be annual. In cool climates, certain 

 grasses behave as winter annuals, living through the winter 

 as small plants and sending up jQower stalks the following 

 spring. So-called "winter" or "fall grasses" behave in this 

 manner. A number of grasses, such as the pernicious quack 

 grass {Agropyron re pens), lawn grass {Poa pratensis), and 

 others, are perennial, i.e., with a course of life extending over 

 three or more seasons. 



Roots. — The root system of grasses is fibrous, that is, 

 composed of numerous slender roots of about equal diameter. 

 No grasses, at maturity, possess a tap-root system, as that 

 of radish, dandelion, beet, and others. In this there is a 

 strong leading central root. The primary roots, those that 

 arise directly from the seed, are temporary, dying after the 

 permanent roots are able to support the plant. The perma- 

 nent roots arise from that portion of the stem which ex- 

 tends from the germinating seed to the surface of the ground. 

 These roots are always produced at about the same distance 

 below the surface, regardless of the depth at which the seed 

 is planted (Fig. 3) . 



Grasses are classed as shallow-rooted plants. However, 

 great variation has been observed in the depth to which the 

 roots penetrate, some extending to depths which cannot be 

 considered as shallow. Roots of buffalo grass {Buchloe) 

 sometimes go to a depth of 7 feet. Rye roots have been 

 found penetrating to a depth of 3 feet, corn 33^ feet (Fig. 

 56), emmer and spelt 3}^ feet, and wheat more than 4 feet. 



Roots may break through the sheaths (that part of the 



