THE ALGAE 173 



cell which enlarges and pushes between the cortical cells. Not all the peri- 

 central cells at the same level behave similarly, but it is quite common to 

 find transverse bands of from four to about six tetrasporangia formed 

 together at one node. Successive nodes generally behave similarlv so that 



Fig. 164. — Ceramium nibruni. A, Procarp branch with trichogyne, on young axis of 

 thallus. Part of a second procarp appears below. B, Procarp after the separation 

 of the auxiliary cell. C to E, Young stages in the development of the gonimoblasts 

 from the auxiliary cell. {After Kylin.) 



tetrasporangia occur in tiers on the branches (Fig. 166). The nucleus of each 

 tetraspore mother cell divides twice, during which meiosis occurs, resulting 

 in the formation of four monoploid nuclei which become arranged around 

 the periphery of the cell. Wall formation is effected bv the ingrowth of 

 partitions from the margin, forming four tetraspores, but the orientation of 

 the walls varies somewhat, both tetrahedral and cruciate arrangements 

 occurring. 



