68 



rLANT 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 • 101). 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- 

 through the extremity of a root of quen t intervals, partitions paral- 



Marsiha. 1 he larjic triangular cell 1 » ' I 



near center of figure is the apical le | t0 tne outer f ace f Qrm s j m j_ 



cell. I lie segments from the inner 



faces may be readily traced back- p u se gments. The division of 



ward; thus the dotted line e< points ° 



to the fourths to the sixth segment tnese sc <r ment S oiveS HSe tO 3. 

 from the posterior n.nht-hand tare "1 ° ° 



apicaiceii. e/>, root -ca P (epiderm.s); s t rU cture covering the very tip 



ec. cortex; c, stele; en, endodermis o • 1 



(pan .,f cortex^; fie , peri. v. i. (part f the root, and connected with 



of stele). Magnified about ioo diam. 

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



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



83). 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 



Fig. 83.— Medial, longitudinal section 



