CHAPTER VI 



PHAEOPHYCEAE 



ISOGENERATAE AND HETEROGENERATAE (EXCLUDING 

 DICTYOTALES, LAMINARIALES AND FUCALES) 



*GENERAL 



The algae composing this group range from minute disks to lOO m. 

 or more in length and are characterized by the presence of a brown 

 pigment, fucoxanthin; the function of this substance is still not 

 clearly understood but it is probably connected with the absorption 

 of light, though not with its utilization (cf. p. 293). In the older 

 classification the group was customarily divided into three orders : 

 the Phaeosporeae (including the Laminariales) with motile gametes, 

 Cyclosporeae with non-motile asexual bodies and non-motile ova 

 and the Acinetosporeae or Tilopteridales with non-motile asexual 

 bodies, the sexual reproductive organs being either absent or 

 imperfect. In 1917 Kylin suggested the following classification: 

 Tilopteridales (Acinetosporeae), Dictyotales, Laminariales, Fucales 

 and Phaeosporeae, this last group really being a polyglot assembly 

 of distantly related forms. Later Taylor (1922) transferred the 

 Laminariales to the Cyclosporeae and placed the Acinetosporeae in 

 the Phaeosporeae thus leaving only two orders. In 1933 Kylin 

 suggested yet another rearrangement with only three groups based 

 upon the type of alternation of generations, but it is doubtful 

 whether this new classification has any more real significance in so 

 far as phylogenetic relationships are concerned. 



(a) Isogeneratae. Plants with two morphologically similar but 

 cytologically different generations in the life cycle, e.g. Ecto- 

 carpaceae, Sphacelariaceae, Dictyotaceae, Tilopteridaceae, Cut- 

 leriaceae. 



(b) Heterogeneratae. Plants with two morphologically and 

 cytologically dissimilar generations in the life cycle: 



I. Haplostichineae. Plants with branched threads, which are 

 often interwoven, and without intercalary growth, e.g. 

 Chordariaceae, Mesogloiaceae, Elachistaceae, Spermato- 

 chnaceae, Sporochnaceae, Desmarestiaceae. 



