4^ 



MORPHOLOGY 



whorls of branches arise. These branches are of two kinds: (i) those 

 of limited growth, the so-called "leaves"; (2) those that resemble 

 the parent axis in indefinite growth. The branches of limited growth 

 form the whorl or rosette of branches at each node ; ^\'hile usually in 

 the axil of one of them the branch of indefinite growth appears. The 

 axillary position of the main branch suggested that the smaller sub- 

 tending branches are leaves. 



The main and lateral axes elongate by means of an apical cell (fig. 

 114), which by successive transverse walls cuts off a longitudinal series 



of cells (segments). Each segment divides 

 transversely into two cells, the lower one 

 of which enlarges, forming the long inter- 

 nodal cell (sometimes 10 cm. or more long), 

 the upper one giving rise by successive di- 

 visions to the plate of nodal cells, which 

 develop the branches. In Nitella the long 

 internodal cells remain uncovered : but in 

 Chara they become covered by a sheath 

 of cells developed from the basal cells of 

 the short branches, so that a cross section 

 of an axis shows a central cell of large 

 caliber sheathed by a ring of small cells 

 (cortical cells). The protoplast of the 

 internodal cell consists of a thick peripheral 

 layer of cytoplasm surrounding a large central vacuole and embedding 

 numerous nuclei and oval chloroplasts. In a young internodal cell there 

 is a single large nucleus, but in connection with the great enlargement of 

 the cell the nucleus gives rise to numerous nuclei by fragmentation. The 

 internodal cells of Nitella are noteworthy for exhibiting streaming 

 movements of protoplasm with remarkable distinctness. 



Reproduction. — No asexual spores are produced, but vegetative 

 multiplication is secured by tuberlike outgrowths, special branches, etc., 

 from the nodes. The structures connected with sexual reproduction, 

 however, afford the most distinguishing feature of the group. The 

 antheridia and oogonia, instead of being single cells, as in the groups 

 previously described, are highly complex structures. They are borne 

 at the nodes of the short branches and are visible to the naked eye, the 

 mature antheridia being deep orange to red (fig. 115). 



Anlheridium. — The antheridium is globular, the wall being com- 



FiG. 114. — Chara: apical 

 cell cutting off .segments to form 

 nodes and internodes; the nodal 

 cells forming branches. — After 

 Sachs. 



