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 nneqiial ])Orlions, so that the smaller is looked 

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

 inner faces Ije numljered respeLti\'ely i, 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 acti\elv di\"iding 

 cells is the p)rimary meristem or 

 growing point of the root (com- 

 pare ^loi). As the older cells 

 of the primary meristem enlarge, 

 divide, and tlifferentiate, they 

 are constanth- pushing the apical 

 cell further awav from the older 

 part. Not only are segments 

 cut from the three inner faces of 

 the apical cell, but, at less fre- 

 quent intervals, jiartitions paral- 



pe 'eji 



Fig. 83. — Median lon^'itudinal .section 

 tlirough tlie extremity of a root of 

 Marsilia. Tile ]ar;^e triangular cell 

 near center of figure is the apical Jgj j^ fj^^ ^^^y^^ f^, f j ; 



cell. The segments trom the inner 

 faces may be readily traced back 

 ward; thus the dotted line fc points 



ar segments. The division of 



to the fourth^ to the sixth segment ^^^^^^ SCl^nnCntS L^MVCS rise tO a 

 from the posterior ng^ht-hand lace nt o t^ ^v, w l^ 



Ti^.- f kX'^Sdenlns Structure co^■ering the ver^• tip 

 Tlxl T^^A^l'^:?:^^:! of the root, and connected with 



-After Van T.eghem. Jj f^j. ^ ^\-^^^^ distance Onlv. It 



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

 <S3). Since the cells of the surface of the root-cap are older 

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

 lie in front of them, thev ser\e to ])rotect the more delicate 



