STRUCTURE AND DEVELOPMENT. 



23 



stem-node, remaining quite short and undergoing 

 division by means of longitudinal septa in the direc- 

 tion of the axis, the lower (d) forming an internode, 

 remaining undivided but lengthening considerably. 

 In this way the stem of a Charophyte presents a 



. 3. Young shoot of Nitella in successive stages (after Giesen- 

 hagen) ( x c. 150). In i the apical cell a is undivided; in ii a 

 portion b has been cut off from its base by a transverse section ; in 

 iii the lower cell b has been subdivided into a stem-node c and an 

 internode d. The young branchlets are shown in each figure 

 crowing out from the lower nodes. 



o o 



particularly well-marked series of nodes and inter- 

 nodes. The internodes consist each of a single 

 elongated cylindrical cell never becoming divided but 

 attaining in some species to the extraordinary length 

 of 20 cm. Torsion is to a greater or less extent 



FIG. 4. Transverse sections of young stem-node of Chara delicatula, 

 showing successive division (after Kuczewski) ( x c. 190). The figures 

 denote the order in which the several cells originate. 



always present, the spiral being invariably dextral 

 and therefore in the opposite direction to that of the 

 enveloping cells of the oogonium. The cortex, with 

 which the internodes of many species are entirely 

 covered, will be described when dealing with the 

 outgrowths from the nodes, to which it properly 

 belongs. 



