40 



Plant Physiology 



of which arise in rather irregular order, but make up a 

 general root-system which may occupy a fusoidal, a coni- 

 cal, or an obconical soil volume. This type includes let- 

 tuce, parsnip, and a 

 great variety of common 

 plants. In the other 

 type there may be little 

 or no indication of a tap- 

 root, and instead few or 

 many lateral roots of 

 more or less equal size 

 may in a way take its 

 place. Corn, for in- 

 stance, possesses at the 

 beginning of germination 

 a distinct tap-root, but 

 very soon, under ordi- 

 nary circumstances, in 

 the soil the length of this 

 may be approached or 

 exceeded by laterals or 

 by whorls of secondary 

 roots originating consid- 

 erably later (Fig. 8). In 

 many of the small cere- 



FIG. . oenerai appearance 01 uie TOOL- i ,1 l j 



system of corn at the time of tasseling. als there are Pduced 



upon germination several 

 roots which may be termed of the first order, and the 

 direction of growth of these determine for many days the 

 general form of the system. 



It is a part of the function of the root-system to fix the 



FIG. 8. General appearance of the root- 



