ZEA MAYS 



ii5 



ears, primary and adventitious root systems — have been suffi- 

 ciently differentiated that their topography can be readily deter- 

 mined. 



The Stem. — The mature stem is a meristele with bundles scat- 

 tered throughout the fundamental parenchyma. The bundles near 

 the periphery of the stem are smaller and more numerous than those 



tran bit 



Fig. 50. Transection of the second internode showing transitional character: co, cortex; 

 ep, epidermis; pfi, phloem; tran hu, transition bundle; xy, xylem. (After Avery.) 



toward the center of the axis. The centrally located parenchym- 

 atous cells are large and thin-walled, with intercellular spaces at 

 their angles. Those adjacent to the epidermis are smaller; and, in 

 the mature stem, become thick-walled and lignified, forming a 

 protective rind inside the epidermis which also lignifies at maturity. 

 The stomata, guard cells, and accessory cells are similar to those 

 of the leaf . (Fig. 15.) 



The node is woody and rigid and its vascular anatomy is very 

 intricate owing to the fact that at each node there is a large number 



