134 BOTANY 



Affinities of Phaeophyceae 



The Phaeophyceae must be considered to be a highly specialized 

 group of plants, whose peculiarities are largely due to their essen- 

 tially marine mode of life. They are very different in most respects 

 from the Chlorophyceae, and it is quite possible that they have had 

 an entirely independent origin. The striking resemblance between 

 the zoospores and gametes of the Phaeophyceae and some of the brown 

 Peridineae suggests the possibility of their having originated from 

 some such forms, which might bear somewhat the same relation to 

 them that the simpler Volvocaceae do to the other Chlorophyceae. 



Classification of Phaeophyceae (Engler and Prantl, 9) 



CLASS 



Ord. 1. Phceosporece. Producing both zoospores and gametes, the 

 latter always motile. 



a. Gametes similar. Families: Ectocarpacese, Sphacela- 



riaceae, Laminariaceae, etc. 



b. Gametes unlike. Families : Cutleriaceae, Tilopterida- 



ceae. 



Ord. 2. Cydosporece (Fucacece) ; no zoospores. 9 gametes non-ciliated. 

 Fam. 1. Fucaceae. 



Dictyotales (Williams, 39) 



This small group of marine Algae is probably related to the 

 Phaeophyceae, and might perhaps be included in that class. The 

 plants grow from a definite apical cell and do not reach a large size, 

 nor is the differentiation of the tissues as perfect as in the higher 

 Phaeophyceae. Until recently, it was supposed that their reproduc- 

 tive cells were always destitute of cilia, and for this reason they 

 have sometimes been included with the Rhodophyceae. Recently, 

 however, motile cells have been found. 



Both sexual and non-sexual reproductive cells are formed, the 

 former showing great difference in size between the male and female 

 cells (Fig. 105). 



CLASS III. RHODOPHYCE^: (RED ALG^E) 



The Red Algae comprise the majority of seaweeds, but in size they 

 are much inferior to the Phaeophyceae. Most of them inhabit salt 

 water, but a number of genera are found in fresh water, usually in 

 cold, rapid streams, or on rocks washed by falling water. In size 

 they range from almost microscopic forms to stout plants a metre or 

 more in length. 



