17 



stem, it gives off, by division, a complex mass of cells which 

 comprise the basilar node of the leaf. From this node are 

 developed the cortex cells and stipules found in Chara, the adventi- 

 tious leaflets (which do not develop nodes like true leaves), and even 

 organs of fructification (especially in the genus Tolypella). 



In the genus Nitella the basilar node of the leaf is much more sim- 

 ple than it is in Tolypella and Chara. In Nitella only a few cells sur- 

 round and support the base of the leaf, and these cells rarely, if ever, 

 give rise to any organs (except to adventitious leaflets in some 

 species, as in our N. clavata). There may be only a circle of four 

 cells, or even in the same species, as in N. flexilis, an indefinite num- 

 ber of cells may develop. 



DEVELOPMENT OF THE CORTEX. From the upper and lower por- 

 tions of the basilar node cells arise, which extend upward and down- 

 ward closely pressed against the central internodal cell of the stem. 

 These cells grow, pari-passu, with the elongating stem cell, they 

 spread laterally, and, as a rule, entirely encircle the stem and form 

 a complete cortex. The first view of these cells is shown in Fig. 



1 8, c and c'. A front view is shown in Fig. 19, c, which repre- 



$ sents the side of a young growing stem ; a 



single cell from above and one from below 

 ~.C cover the internode vertically, and, with the ad- 

 jacent cells, completely encircle the stem. As the 

 internodal cell of the stem elongates these cells 

 Fig. I9 . elongate and develop nodes and internodes, and, 



when fully developed, give off lateral cells. Since the leaves of 

 successive verticils are not directly over each other, but diverge 

 to the extent of half the distance between the leaves, the cortex 

 cells which extend upward and downward from the base of each 

 leaf (except that the oldest leaf of each verticil develops a shoot in 

 its axil instead of a cortex cell, causing one cortex cell less in the 

 encircling series which ascends from a vertical, than in the series 

 which descends), alternate, and in the centre of the internode they 

 interdentate, as shown in Fig. 20, which represents an elongating 

 cortex system. Each " c " in this figure represents a single cortex 

 " lobe," which has developed from a single cell, as shown in Fig. 



19. In Fig. 20 these cortex cells (four above and three below), 

 have begun the development of nodes and internodes; "in" the 

 internodal cells, and "n," "en," "n," the node; "en" the central 



