VI.] STONEWORTS. 43 



division into several smaller cells by the development of 

 longitudinal septa. This is the most newly-formed node. 

 Below this again is a single cell, which is both longer and 

 broader than those at the apex, and is an internodal cell. 

 Below it follows another node, composed of more numerous 

 small cells than in the first. Some of the peripheral cells of 

 this node are undergoing growth and division, and thus give 

 rise to cellular prominences, which are the rudiments of the 

 first whorl of leaves. In the still lower parts of the stem the 

 internodal cells get longer and longer, but they never divide. 

 The nodal cells, on the other hand, multiply by division, but do 

 not greatly elongate. From the first, the nodal cells overlap 

 the internodal cell, so as to meet round its equator, and thus 

 completely invest it externally. And, as the internodal cell 

 grows and elongates, the overlapping parts of the nodes 

 increase in length and become divided into internodal and 

 nodal cells, which take on a spiral arrangement, and thus 

 give rise to the cortical layer. 



Thus the whole plant is composed of an aggregation of 

 simple cells ; and, while it lives, new nodes and internodes 

 are continually being added at its summit, or growing point. 

 The internodal cells which give rise to the centre of the 

 stem undergo no important change, except great increase 

 of size, after they are once formed. The nodal cells, on 

 the contrary, undergo division with comparatively little in- 

 crease in -size. And out of them, the nodes, the cortical 

 layer, and all the appendages, are developed. 



In all the young cells of Chara a nucleus of relatively 

 large size is to be seen imbedded in the centre of the 

 protoplasm, which is motionless, and is inclosed in a struc- 

 tureless cell-wall, containing cellulose. As the cell grows 

 larger, the centre of the protoplasm becomes occupied by a 

 watery fluid, and its thick periphery, which remains applied 

 against the cell- wall, constitutes the wall of a sac, or 



