174 A TEXTBOOK OF THEORETICAL BOTANY 



Paraspores are formed in some species, though not in Ceramiiim rubrum. 

 They arise from undivided superficial cells of the cortex and are only formed 

 on the tetrasporic plants. Their germination has not been followed. 



The tetraspores are liberated through the gelatinous covering of the 

 thallus as oval bodies which, on reaching a suitable rocky substratum, divide 

 into two cells. The lower or basal cell elongates and forms a rhizoid, whose 

 terminal extremitv becomes thickened and flattened and develops into a tiny 



Carpo- 

 spores 



Tetraspoi- 

 angium 



Fig. 165. — Ceramium ruhrtim. Cystocarp with 

 carpospores. 



Fig. 166. — Ceramium rubrum. 

 Branch with embedded tetra- 

 sporangia. 



adhesive disc. The upper cell functions as an apical cell, cutting oflF a row of 

 cells which forms the central axis of the new sexual plant. 



Ceramium rubrum therefore shows the same diplobiontic alternation of 

 generations, as we have seen in other members of the Rhodophyceae (see 

 Polysiphonia, p. 168). 



Cryptonemiales 



The Cryptonemiales are Rhodophyceae in which there are definite unions 

 formed between the auxiliary cells and the cells of the vegetative thallus, 

 which not only serve for nourishment but also form the starting points of 

 the gonimoblast filaments. The result is, in many genera, that an elaborate 

 carposporophyte tissue develops within the tissues of the gametophyte, 

 and the carpospores which arise from the gonimoblasts may be located 

 at positions remote from the procarp branch. The auxiliary cells develop 

 on special filaments before fertilization and are actively associated with the 

 post-fertilization changes. 



