30 



PLANT LIFE. 



35. Cortex. — Nitella and Chara are much alike, except 

 that in Chara the main axis and all its branches are composed 

 of a row of large cells, surrounded by a jacket of smaller ones 

 (fig. 37). The walls of these outer cells are often much 

 thickened, and incrusted with salts of lime to such an extent 

 as to render the axis very brittle. Around the main axis the 

 cell-jacket is of much complexity ; it becomes more simple 



Fig. 37. 



Fig. 38. 



Fig. 37. — Transverse section of the axis of Chara. a, internodal cell; £, cortical cells 

 Magnified about 30 diam. — From a drawing by C. E. Allen. 



Fig. 38. — Longitudinal section of apex of axis of Chara. x, apical cell. The seg- 

 ment next below will divide into a nodal and an internodal cell ; the next one has 

 already divided and the nodal half has again divided into two internal and several 

 external (only 2 show) nodal cells, c, d, internodal cells ; between them a node pro- 

 ducing the branches (" leaves ") e and/i and the cortical branches a, a. b, a similar 

 branch growing up from node below, only its tip showing. Magnified 330 diam. — 

 After Sachs. 



upon the whorled branches, and is wanting upon the ultimate 

 divisions. 



While a cross-section of the axis shows a complete union 

 between the walls of the cortical cells (5, fig. 37) and the 

 central one (a, fig. 37), a study of their development shows 

 that they are originally branches of the outer cells at each 

 node, which likewise produce the circle of " leaves." The 



