i8 



Fig. 20. 



nodal cell. The" internodal cells elongate to 

 keep pace with the growing stem; they do not 

 divide ; the nodal cell, however, divides at 

 first into three, a central cell and two lateral cells 

 (Fig. 20, "n," "n" and "en"). The central 

 cell then divides into deep (lying next the 

 stem) and superficial cells. The superficial 

 central cell is the only one which develops 

 spines, or papillae, so that whenever a spine is 

 seen on the stem, we may be sure that it 

 arises from the central node of the cortex. In 

 this way the main cortex series is always to be 

 distinguished, since the lateral cortex cells 

 never develop nodes or spines. This central 

 cell may grow out into a single spine, or it may 

 subdivide into a number of cells and develop a 

 bundle of spines, as in Ch. crinita. In many species which develop 

 but a single spine, or papilla, from the node of the cortex, great 

 variability is observed ; some varieties having numerous spines 

 quite long, while other forms of the same species have almost smooth 

 stems; this is particularly noticeable in Ch. fcetida, A. Br., and Ch. 

 intermedia; our very common Ch. fragilis, with a completely devel- 

 oped triple cortex, rarely produces any spines, or even papillae ; while 

 our forms of Ch. gymnopus, with an equally developed cortex, some- 

 times have numerous spines, as in sub-species elegans; sometimes 

 have nearly smooth stems, as in sub-species Michauxii. 



The development of the lateral cells of the cortex-node marks im- 

 portant groups in the classification of the species of Chara. When 

 the lateral cells develop fully, each cell protrudes from the side of 

 the node and extends longitudinally, forming a long cell lying by the 

 side of the central internodal cell of the cortex and parallel to it. If 

 each lateral cell of the node develops, the cortex "lobe" (the full 

 development of each original cortex cell) becomes composed of the 

 central cell, with its node (and spine) and two lateral cells, forming a 

 triple series. Since one cortex cell arises at the base of each leaf, it 

 follows that there will be (as in Ch. fragilis) three times as many cells 

 surrounding the main internodal cell of the stem as there are leaves, 

 and the stems are said to be " triplasliche corticate" (triple corti- 

 cated). 



Fig. 21 (drawn from nature) is taken from the centre of a young 

 growing internode of Ch. fragilis; the development is nearly perfect, 

 showing the growing lateral tubes from each side of each node ; 



