DESCRIPTIVE TERMS 



357 



Secondary root systems take their rise either from the main pri- 

 mary root or from the underground part of the stem (Fig. 211). 



Both primary and sec- 

 ondary roots may be 

 either fleshy or fibrous 

 in form, and surface or 

 deep, according to their 

 method of distribution 

 in the soil. 



Adventitious roots arise 

 from stems or leaves 



and are thus not lateral 

 FIG. 211. Branching root system of corn 



branches irom a primary 



or a secondary root system. Adventitious roots 

 are especially common in the monocotyledons. 

 Roots are also classified according to the 

 medium in which they grow ; for example, 

 soil roots, water roots, and air roots (or aerial 

 roots'). Air roots are common in corn as prop 

 roots, growing from a node above the ground 

 and later penetrating the earth as brace roots. 



REPRODUCTIVE PARTS AND PROCESSES 



Inflorescence. The inflorescence has already 

 been defined as a cluster of 

 flowers, to distinguish it from 

 solitary flowers borne singly in 

 the axils of ordinary leaves 

 (Fig. 212, A). Some of the 

 main types of inflorescence are 

 indicated in Fig. 213. In this 

 figure the flowers are indicated 

 by circles at the ends of the 

 stems, or peduncles, which arise 

 from the axils of bracts. All of the main types of inflorescence can 

 be derived from the raceme if we suppose certain modifications to 



FIG. 212. Solitary flowers and cluster 



A, axillary and solitary flowers of the 



pimpernel; E, raceme of red currant; 



p, axis of inflorescence; p', peduncle; 



br, bract 



