DIV. I 



THALLOPHYTA 



419 



show a similar segmentation into long internodal cells and nodal cells 

 that are laterally displaced. Branching takes place at the nodes. 



Both the main and lateral axes grow in length by means of an apical cell, from 

 which other cells are successively cut off by the formation of transverse walls. 

 Eacli of these cells is again divided by a transverse 

 wall into two cells, from the lower of which a long 

 interuodal cell develops without further division ; 

 while the upper, by continued division, gives rise 

 to a disc of nodal cells, the lateral axes, and also, 

 in the lower portion of the main axis, to the rhizoids. 

 In the genus Xitella the long internodes remain naked, 

 but in the genus Chara they become enveloped by a 

 cortical layer consisting of longitudinal rows of cells 

 which develop at the nodes from the basal cells of the 

 lateral axes. A corresponding construction is found 

 among other Thallophyta in certain Brown Algae (e.g. 

 Spertna tochnus). 



Each cell contains one normal nucleus derived 

 from a karyokinetic division. As a result of 

 the fragmentation of its original nucleus, how- 

 ever, each internodal cell is provided with a 

 number of nuclei which lie embedded in an 

 inner and actively -moving layer of parietal 

 protoplasm. Numerous round chloroplasts are 

 found -in the internodal cells. 



Asexual reproduction by means of swarm- 

 spores or other spores is unrepresented in the 

 Characeae. Sexual reproduction, on the other 

 hand, is provided for by the production of egg- 

 cells and spermatozoids. The female organs are 

 ovate. They are visible to the naked eye, and, 

 like the spherical red-coloured anthericlia, are 

 inserted on the nodes of the lateral axes. With T 



FIG. 361. Chara fragilis. End 



the exception of a few dioecious species, the O f main shoot, (Nat. size.) 

 Characeae are monoecious. The fertilised egg- 

 cell develops into an oospore. The Characeae thus exhibit no altera- 

 tion of generations but a succession of gametophytes. 



The male organs (Fig. 362 A) are developed from a mother cell 

 that first becomes divided into eight cells. Each octant by two 

 tangential walls gives rise to three cells. In this way are derived the 

 eight external tabular cells of the wall, the cavities of which are in- 

 completely partitioned by septa extending in from the cell wall ; the 

 eight middle cells form the manubria and become elongated ; the eight 

 innermost cells assume a spherical form as the primary head cells. 

 Owing to the rapid surface growth of the eight shield cells a cavity 

 is formed within the male organ into which the manubria bearing the 



