174 



CHARACE/E 



the large terminal cell is exposed. In addition to the leaves there 

 spring, from the basal nodes of some species of Chara (L.), other leaf- 

 like structures known as stipules, one, two, or three in connection with 

 each leaf. The stipular cells are always undivided 

 by septa, and arise as papillae on the cortical 

 cells. 



The cortex of the stem and branches is de- 

 veloped out of the nodal plate of cells ; the 

 upward and downward prolongations from the 

 nodes usually meeting about the middle of each 

 internode, where they dovetail into one another. 

 These cortical internodal cells do not, however, 

 like the axial cells, remain entire ; they divide, 

 both transversely and longitudinally, into three 

 parallel rows of cells, the central row of each 

 series being somewhat elevated into a ridge. 

 The mode and extent of development of the 

 cortical cells vary according to the species. 

 The number of leaves in a whorl 

 is usually from four to ten. At 

 the lower part of the main stem 

 the internodes are shorter, and 

 from the nodes spring rhizoids 

 or rooting filaments which serve 

 to fix the plant in the soil, con- 

 sisting of long hyaline nearly undi- 

 vided tubes, which grow obliquely 

 downwards, and lengthen only at 



their apex. The rhizoids are 

 always trichomic, springing from 

 superficial cells. 



The nearly hemispherical 

 apical cell of the terminal bud of 

 the stem first divides by a trans- 

 verse wall into a new apical cell 

 and a disc-shaped segment-cell. 

 Each se g ment then a g ain divides 

 by a wall parallel to the first; 

 the lowest of these does not again divide, but develops into the axial 

 internodal cell, while the upper one undergoes vertical division, and be- 

 comes a node. Each successive whorl on the main stem alternates with 

 those immediately above and below it, so that the oldest leaves of a 



FIG. 160. Chara fragilis 

 Desv. (natural size). 



nified) L> (mag ' 



