FUCALES (HETEROGENERATAE) 201 



activity of one of the tertiary apicals. Subsequently the secondary 

 apical, A^, undergoes a series of divisions, thus producing a row of 

 apical cells each of which develops into a fertile branchlet. The 

 tertiary apical normally only gives rise to the leaf blade, but it may 

 divide again sometimes to give a new shoot or a series of fertile 



Fig. 134. Seirococciis. A, plant of S. axillaris with fruiting laterals. B, diagram 

 to show method of branching, b^-hf, blades, b^ being the youngest. C, diagram 

 showing disposition of apical meristematic cells, A-A3, the former being the 

 oldest: / = origin of leaf organ. D, E, paraphyses of female conceptacle ( x 135). 

 F, megasporangium ( x 135). (A-C, after Oltmanns; D-F, after Murray.) 



branchlets which will thus appear to grow out from the main 

 thallus. 



LORIFORMES 



*Fucaceae: Himanthalia{himant, thong;halia, of the sea). Fig. 135. 

 The short, perennial frond or button arises from a small disk- 

 like holdfast, the shape of the button being dependent upon level 

 because it is short and stumpy when it grows exposed at high 



