136 JOHN H. SCHAFFNER Vol. XXII, No. 5 



18. Cenocytic algse, septate or nonseptate. 19. 



18. NotcenocytiCjbutwithnormalcellshavingasinglenucleus. (Conferve^). 23. 



19. Vegetative body usually septate, consisting of a series of cenocytes; chloro- 



plasts forming a net, rarely in separate plates. (Siphonoclade^). 20.. 



19. Vegetative body usually nonseptate, with distinct lenticular, oval, or plate- 



like chloroplasts. (Siphone.«). 21. 



20. Filanrents branched; plants isogamous. Cladophorales. 



20. Filaments unbranched, free-fioating; plants heterogamous with stationary 



eggs. Sphaeropleales. 



21. Isogamous, or sexual reproduction unknown. 22. 



21. Sexual reproduction by highly specialized stationary eggs and motile sperma- 



tozoids; thallus tubular, branched or unbranched. Vaucheriales. 



22. Small globular terrestrial plants with branched rhizoids penetrating the 



ground; zoospores with cilia of unequal lengths or with only one. 

 Botrydiales. 



22. Mostly large marine or sometimes endophytic algae; zoospores if present 



otherwise. Bryopsidales. 



23. Isogamous, or the free-swimming gametes of unequal size. 24. 



23. Heterogamous, the egg stationary in the oogonium; oogonium developing a 



cortical layer after fertilization, or if not then certain cells of the filament 

 with peculiar striate rings around the top. 28. 



24. Thallus unbranched. 25. 



24. Thallus filamentous, branched, usually abundantly so, the branches often 



with hair-like attenuated tips. Chaetophorales. 



25. Chloroplasts reticulate, without pyrenoids; growing in fresh water. 



Microsporales. 



25. Chloroplasts central or parietal, with one or more pyrenoids. 26. 



26. Chloroplast single, central, stellate, with one pyrenoid; no zoospores known; 



aerial in habit. Prasiolales. 



26. Chloroplasts parietal with one to many pyrenoids. 27. 



27. Unbranched filaments; chloroplasts with one to many pyrenoids. Ulotrichales. 



27. Thallus expanded, a 1-2-layered lamina or tube; chloroplast single with one 



pyrenoid; mostly marine plants. Ulvales. 



28. Oogonium not developing a cortical layer after fertilization; zoospores with 



a crown of cilia; certain cells with striate rings at the upper end. 

 Oedogoniales. 

 28. Oogonium with a trichogyne-like tip, covered after fertilization by a cortical 

 layer; thallus disk-like or cushion-like; zoospores biciliate. Coleochaetales. 



29. Mostly marine brown algae; isogamous or with ciliated sperms, and large eggs, 

 both gametes discharged from the gametangia; or with zoospores only. 30. 



29. Mostly marine red algae, with stationary eggs and non-ciliated sperms; 



mostly with tetraspores; zoospores absent; usually with cj'stocarps. 35. 



30. Zoospores present; sexual reproduction by motile biciliate gametes produced 



in external gametangia; occasionally heterogamous, the extreme cases 

 with non-motile eggs. (Phaeospor.*:). 31. 



30. Zoospores absent; sexual reproduction by means of motile sperms and non- 



motile eggs which are discharged from the oogonium; gametangia sunken 

 or external; non-sexual reproduction absent or by means of nonmotile 

 spores. 84. 



31. Zoospores and isogametes similar and motile. 32. 



31. Zoospores and heterogametes dissimilar. 33. 



32. Frond various, simple or branched, but never differentiated with definite 



root-like and leaf-like parts. Ectocarpales. 



32. Frond large, leather-like, usually stalked, differentiated with root-like and 



leaf-like parts; with zoospores only; plants usually very large. Laminariales. 



33. Gametes large and small but both motile; plants medium to large, fiat, 



branched, or orbicular, attached by rhizoids. Cutleriales. 

 33. Gametes a small active spermatozoid and a nonmotile egg; fronds filiform, 

 tufted, attached by rhizoids. Tilopteridales. 



