244 



STRUCTURE AND LIFE HISTORIES 



antheridium continues to divide until as many as 1,500 or 

 more sperms are formed in each one. Since the antheridia 

 occur in groups of sori (Figs. 178 and 179), the total num- 



FIG. 178. Dictyota dichotoma. Cross-section of a male thallus, show- 

 ing the comparative development of the antheridial sori, and the tufts of 

 hairs which are scattered over the frond, a, young sorus; 6, older sorus; 

 c, sorus opened. The sperms have been set free. There remain only the 

 cells which form the involucre, d, tuft of very young hairs; e, tuft of 

 older hairs; /, the same fully developed. X about 35. (After Thuret.) 



FIG. 179. Dictyota dichotoma. A, vertical section through portion 

 of sorus, showing antheridia; B, sperms. (Redrawn from J. Lloyd Wil- 

 liams.) 



her of sperms formed on one plant, or even in one sorus, 

 is enormous. The oogonia may occur singly or in groups 

 (Fig. 180), 



