FUCALES (HETEROGENERATAE) 205 



or dioecious, the conceptacles being borne in terminal or intercalary 

 positions on the ramuli, and, as in some of the other genera, only one 

 ovum develops in each megasporangium, the remaining seven nuclei 

 degenerating. In the seedling the main shoot is very short and soon 

 stops growth, and as a consequence it is completely overtopped by 



Fig. 137. Cystoseira. A, C. ericoides, plant ( x i). B, portion of same enlarged 

 ( X 4-5). C, germling. D, same, rather older. E, diagram to show nature of 

 branching in C. ahrotanifolia. (A, B, after Newton; C-E, after Oltmanns.) 



the lateral branches. The first two shoots arise opposite each other 

 but the remainder have a divergence of 2/5. The genus is principally 

 confined to the warmer subtropical and temperate waters of the 

 globe. 



*Sargassaceae: Sargassum {sargasso^ Spanish for sea- weed). Fig. 

 138. 



- The branching in this genus is radial with a divergence of 2/5. 

 The primary branch is a sterile phylloclade which bears cr)^pto- 

 stomata whilst the secondary branch is also sterile and is commonly 

 reduced to an air-bladder. In some species there may be yet a 



