180 University of California Piiblicatioyis in Botany [^ol. 8 



De-Toni, Syll. Alg., vol. 1, part 1, 1889, p. 264. Cladophorem 

 Hassall, Brit. F. W. Algae, vol. 1, 1845, p. 213. 



The family of the Cladophoraeeae is understood in various ways, 



but it has seemed best to understand it in the sense used by Oltmanns 



(1904, p. 255) and by Collins (1909, p. 321). It includes all the forms 



of the strictly filamentous Siphonocladiales which are either simple 



or, if branched, have branches which are septate at their bases, usually 



with no distinct main axis in the branched forms, and with all axes 



of indefinite growth. Thus we include Microdictyon, Boodlea and 



Anadyomene. Possibly Struvm also should be included in this family 



but it has a very distinct main axis and lateral axes of definite growth. 



In these respects Struvea resembles the Dasycladaceae, but it differs 



from the members of this family in its lack of calcification and of 



specialized zoosporangia (or gametangia) while it differs from the 



members of the Siphonocladiaceae (in the narrower sense) by having 



septa at the the bases of the branches. In Cladophoropsis, there occur 



more or less basal septa, but more frequently they are absent. We 



have followed West (1916, p. 305) in referring Gomontia to the 



Ulotrichales. 



Key to the Genera 



1. Filaments simple 2 



1. Filaments branched 6 



2. Filaments usually stiff or rigid 3 



2. Filaments flaccid 5 



3. Filaments large, over lOOyu diam 12. Chaetomorpha (p. 198) 



3. Filaments smaller, under 100/x diam 4 



4. Filaments attached 12. Chaetomorpha (p. 198) 



4. Filaments unattached, prostrate 10. Rhizoclonium (p. 180) 



5. Filaments attached 11. Hormiscia (p. 187) 



5. Filaments unattached, prostrate 10. Rhizoclonium (p. 180) 



6. Branches free 7 



6. Branches anastomosing, forming a network 15. Microdictyon (p. 231) 



7. Filaments not held together by special rhizoidal or hooked branchlets 



13. Cladophora (p. 207) 



7. Filaments held together by special rhizoidal branchlets or by hooked branchlets 

 or by both 14. Spongomorpha (p. 220) 



10. Rhizocloiiium Kuetz. 



Filaments usually prostrate, or slightly ascending, of a single series 

 of segments, unbranched, or occasionally slightly branched, with few 

 to many rhizoidal branchlets composed of one to few segments ; seg- 

 ments with one to several nuclei (rarely one) and a single reticulate, 

 parietal chromatophore with numerous, more or less regularly spaced, 



