Fig. Ii6 Himanthalia lorea. A, fertile plant. B, C, abnormal 

 buttons. D, button from bottom of dense zone. E, button from top 

 of dense zone. F, T.S. apical cell. G, L.S. behind apex of young 

 receptacle. m=meristoderm; s.c.= cells recently cut off from it; 

 o.c. =outer cortex; i.e. =inner cortex; m =medulla; p =pit. H-K, 

 stages in elongation of medullary cells ( x 125). L, mature mega- 

 sporangium (oogonium). (A-E, I, after Gibb; F-H, after Naylor.) 



the extremely elongated cells of the medulla may take on an ap- 

 pearance resembling the trumpet hyphae of Laminaria. This may 

 be a case of parallel development, but in view of other similarities 

 to Durvillea it may be suggested that Himanthalia represents a 

 primitive though somewhat speciaUzed member of the Fucales. 

 Reduction has proceeded so far in this genus that only one ovum 

 matures in the ripe oogonium (macrosporangium). Liberation of 

 gametes is controlled by the tides and exposure, and there is a 

 definite periodicity related to these two factors. 



207 



