Fig. ii8 Sargassum. A, S. filipendula ( x 0-45). B, base of plant. 

 C, escape of sporangia each with eight nuclei ( x 40). D, seedling at 

 rhizoid stage ( x 105). E-G, stages in branching, 5. thunhergii 

 ( X 0-22). a =main initial, a^ = branch initial, a^, = secondary branch 

 initial. (A, B, after Taylor; C, after Kunieda; D, after Tahara; 



E-G, after Oltmanns.) 



eight eggs may develop. In tiie former case the single ovum con- 

 tains all eight nuclei, but only one of these grows larger and is 

 actually fertihzed. This state of affairs can be interpreted as a 

 failure on the part of the megaspores and gametophytes to form 

 cell walls, and is a secondary condition due to still further reduc- 

 tion. In S. filipendula there is no stalk to the young megasporangium 

 and so it is embedded in the wall of the conceptacle. When ripe the 



210 



