GROUP I. THALLOPHYTA : AUGJE. 261 



pheral nodal cells keep pace with the growth of the internodal cells, 

 forming the cortex over them. 



The leaves and branches of the stem are all developed from the cells of 

 the nodes ; the leaves spring in a whorl, one from each of the peripheral 

 cells of the node, and the branches are developed as buds in the axils of 

 one or more of the leaves of each whorl. 



The mode of growth and general morphology of the leaf is essentially 

 the same as that of the main stem or one of its branches ; it grows by 

 means of an apical cell resembling that of the stem, and from the seg- 

 ments are formed nodes and internodes in regular succession ; from the 

 nodal cells of the leaf arise whorls of leaf-branches or leaflets. The only 

 fundamental difference between the leaf and the stem of the Characese is 

 that, whereas the apical growth of the latter is unlimited, that of the 

 former is limited ; the apical cell of the leaf at length ceases to' divide, 

 assuming a somewhat cylindrical form with a pointed tip. 



The roots, with the exception of the first root of the embryo, are all 

 adventitious, being developed from the lower nodal cells of the stem. 

 They are simpler in structure than the stem or leaf, each consisting of a 

 colourless filament of long, narrow cells; the growth is apical, though the 

 apical cell is not specially differentiated as in the stem; the cells of the 

 root are connected in a peculiar manner, the contiguous ends of the two 

 cells having each somewhat the shape of the sole of a human foot ; root- 

 branches are developed from that portion of the cell, just above the articu- 

 lation, which corresponds to the heel ~>f the foot. 



The sexual organs (Fig. 150) are in all cases borne on the leaves ; the 

 antheridium is developed from the terminal cell of a leaf or of a leaflet ; 

 the oogonium replaces a leaflet. The plant may be either monoecious or 

 dioecious. 



The antheridium is a spherical body, of a green colour when young, but 

 orange when mature, borne on a stalk. Its wall consists of eight cells, 

 each of which is termed a shield, presenting marginal infoldings of the 

 wall ; the wall of the upper half of the antheridium consists of four tri- 

 angular shields ; that of the lower half consists likewise of four triangular 

 shields, each of which has its lower angle truncated to admit of the 

 passage of the stalk-cell. On the inner surface of each shield, at its 

 centre, is attached a cylindrical cell, the manubrium, which extends to 

 near the centre of the antheridium. Each manubrium bears at its inner 

 end a somewhat spherical cell, the capitulum. To each capitulum are 

 attached usually six rounded cells, the secondary capitula. Connected with 

 each secondary capitulum are two cells, each of which bears a pair of long 

 filaments, each filament consisting of about two hundred cells. The cells 

 of the filaments are the mother-cells of the spermatozoids, each cell giving 

 rise to a single spermatozoid. 



The male cell or spermatozoid consists of a club-shaped spirally-wound 

 mass of protoplasm bearing two long cilia at its pointed anterior end. 

 When the antheridium is mature the shields separate, the spermatozoids 

 are set free from their mother-cells and escape into the water. 



The oogonium is the enlarged terminal cell of the leaflet which it repre- 



