136 



BOTANY 



cells are connected by very evident protoplasmic filaments (Fig. 106). 

 There is a large pit in the middle of the division-wall, which is 

 closed by a thin membrane, on each side of which is a thick plate of 

 a substance somewhat like the mucilage masses in the sieve-tubes of 

 the higher plants. The actual communication is effected by delicate 

 pores around these plates, through which fine threads connect the 

 neighboring protoplasts. 



In the young cells there is always a single nucleus, but the older 

 cells, which are often large, frequently possess numerous nuclei. 

 The cell-walls show a tendency to become gelatinous, and there may 

 be developed an abundant intercellular gelatinous substance in which 

 the cells appear to be imbedded. 



D 



FIG. 106. A-C, Callithamnion floccosum. A, cells showing the connection between 

 the protoplasts ( X 600) . B, young, C, mature, tetrasporangia (X 250). D, poly- 

 sporangium of C. dasyoides. 



Apical Growth. The growth of the plant is, with few exceptions, 

 apical. In the more delicate forms there is a single apical cell : in 

 the larger ones there may be a group of these (e.g. Champia). When 

 there is a massive thallus, it can usually be shown to be composed of 

 extensively branching filaments congenitally united by the tenacious 

 intercellular substance, and in such cases each of the individual 

 branches has its own apical cell. Ordinarily the cells divide no fur- 

 ther, but in Nitophyllum and the Corallines there are intercalary 

 divisions. 



Reproduction 



A marked characteristic of the Rhodophycese is the complete 

 absence of ciliated cells. Non-sexual reproduction is usually effected 

 by the so-called Tetraspores, which, as their name indicates, are formed 



