62 



At its base the primordial cell has annular constrictions 

 and the wall here is very thick and stratified (Fig. 45), higher 

 up the cell wall is smooth and rather thin (Fig. 49). 



Fig. 11. Siphoitocladus tropicus (Crouan) J. Ag. 

 a, young plant: b, c, d, different parts of filaments. (About ]i):l). 



When the young cell has reached a certain degree of mat u- 

 rity, it is divided by segregative cell-division. The whole cell 

 contents (protoplasm with nucloi, chromatophores etc.) are divi- 



