Meristems 



79 



Fig. 4-18. Median section of root tip of Zea, showing the quiescent center (stippled). 

 Its cells are physiologically different from the surrounding ones and seem rarely to 

 divide or grow. ( From Clowes. ) 



for the normal preponderance of roots at the base of the plant axis. A 

 high carbon-nitrogen ratio (p. 366) also favors root growth. Torrey ( 1950) 

 presents evidence that a growth substance, not auxin, is produced in the 

 root and moves toward the apex, stimulating the formation of lateral 

 roots. 



Intercalary Meristems. Growth of an axis in length may sometimes take 

 place at other points than its tip, by the activity of an intercalary meristem. 

 Thus in many monocotyledons cell division persists in the base of an 

 internode when it has ceased elsewhere, and the stem elongates all along 

 its course, somewhat like an extending telescope (Prat, 1935). The gyno- 

 phore of the peanut, which carries the young fruit down and into the 

 ground, grows in a somewhat similar way, as has been described by 

 Jacobs (1947). Such material is excellent for a study of the relations of 

 cell division and cell elongation to growth. 



LATERAL MERISTEMS 



The Vascular Cambium. Apical meristems govern growth in length and 

 produce those tissues commonly called primary. Their cells tend to be 

 arranged in longitudinal rows, each row being the descendants of a single 



