68 



PLANT LIFE. 



initial, cell. It is situated with one face directed toward the 

 apex of the root (see fig. 83), and the other three faces 

 within it. Parallel to the three inner faces partitions are 

 constantly formed in regular succession dividing this apical 

 cell into two unequal portions, so that the smaller is looked 

 upon as a segment cut off from the larger portion. If these 

 inner faces be numbered respectively 1, 2, 3, the segments 



are constantly produced in the 

 order of the numbers. These 

 segments themselves divide to 

 form other cells, and thus give 

 rise to all the tissues of the root. 

 This mass of actively dividing 

 cells is the primary meristem or 

 growing point of the root (com- 

 pare ^[10 1). As the older cells 

 of the primary meristem enlarge, 

 divide, and differentiate, they 

 are constantly pushing the apical 

 cell further away from the older 

 part. Not only are segments 

 cut from the three inner faces of 

 the apical cell, but, at less fre- 



Fig. 83. — Median longitudinal section 



M«:t^X^VL^'c°n quent intervals, partitions paral- 



lei to the outer face form simi- 

 lar segments. The division of 

 these segments gives rise to a 

 structure covering the very tip 



near center of figure is the apical 

 cell. The segments from the inner 

 faces may be readily traced back- 

 ward; thus the dotted line ec points 

 to the fourth, c to the sixth segment 

 from the posterior right-hand face of 

 apical cell, ep, root-cap (epidermis); 

 ec. cortex; c, stele; en, endodermis 



^£US^KS^ C dK of the root, and connected with 

 -After Van Tieghem. it for a short distance only. It 



receives, therefore, the appropriate name of root-cap (ep, fig. 

 8^). Since the cells of the surface of the root-cap are older 

 and firmer than the inner segments and the initial cell, and 

 lie in front of them, they serve to protect the more delicate 



