1 68 



PHAEOPHYCEAE 



macroscopic plant is an annual, being abundant in the colder 

 waters of both hemispheres. 



'k^^Slii:j^B 



Fig. 113. Chorda Filum. A, plant ( x |). B, transverse section, high-power, with 

 sporangia. C, female gametophyte ( x 145). D, male gametophyte (X175). 

 (A, original; B, after Oltmanns; C, D, after Kylin.) 



Desmarestiaceae : Desmarestia (after A. G. Desmarest). Fig. 114. 



The plants are bushy and usually of some considerable size, 

 especially the species found on the Pacific coast of North America. 

 They sometimes bear gall-like swellings which are caused by a 

 copepod, and similar galls caused by the copepod Harpacticus 

 chelifer have been recorded from the red alga Rhodymenia palmata. 

 The erect, cylindrical or compressed thallus arises from a disk-like 

 holdfast and exhibits regular pinnate branching, the branches either 

 being elongate or else mere denticulations. The elongate branches 

 terminate in much-branched uniseriate filaments, which are also to 

 be found on the denticulations, but as these filaments are deciduous 

 the plants have a definite winter and summer aspect. Morpho- 

 logically, the thallus is composed of a single prominent central row 



