204 



PHAEOPHYCEAE 



Fig. 136. Halidrys siliquosa. A, plant ( x |). B, apex to show branching, 

 a = primary initial, ai-a4 = secondary initials. (A, original; B, after Oltmanns.) 



Sargassaceae : Cystoseira (cysto, bladder; seira, chain). Fig. 137. 



The much-branched perennial thallus is either cylindrical or 

 compressed and arises from a fibrous woody holdfast which has 

 more or less the structure of a conical cavern. The primary 

 branches arise from the main stipe towards the base and divide 

 above into filiform branches and branchlets, but when the latter do 

 not develop very far one gets what is known as the ''Erica" and 

 '' Lycopodium" types, so called because of their resemblance to 

 members of those genera. Seriate rows of small air vesicles may be 

 inserted in the branches, and when this occurs the row of vesicles 

 must be regarded as a modified branch. The plants are monoecious 



