390 University of Calif ornia PuMications in Botany [Vol. 8 



in others they occur but seldom. What our increasing knowledge may 

 teach us concerning these seemingly exceptional forms must be left for 

 future consideration. The typical members of the Phaeosporeae possess 

 unilocular zoosporangia and plurilocular gametangia and have the 

 gametophyte and sporophyte of very closely similar size and struc- 

 ture. Some scattering genera and species are only known to produce 

 the unilocular zoosporangia, while others produce only the plurilocular 

 gametangia, but, considering seemingly close affinities in these puzzling 

 cases, it seems undesirable for the joresent, at least, to refer either 

 elsewhere than to the Phaeosporeae. They may be found to repre- 

 sent either imperfect, or perhaps even dimorphic forms, when their 

 development shall have been carefully studied. The Laminariales, 

 which we still include under the Phaeosporeae, were long known only 

 with unilocular sporangia producing biciliated zoospores, but have 

 recently been found also to possess a microscopic gametophyte with 

 decidedly modified (unilocular) gametangia producing either non- 

 motile egg cells (or oospheres) or biciliated sperms. The Phaeosporeae 

 may be distinguished from the Acinetosporeae by the lack of aplano- 

 spores, and from the Fucales by the possession of either known zoo- 

 sporangia or plurilocular gametangia or both. 



Key to the Orders 



1. Gametangia present on macroscopic plants (zoosporangia known or unknown). ... 2 

 1. Only zoosporangia present on macroscopic plants (gametangia known, or 



suspected of being, on microscopic plants) 3 



2. Terminal cell present and conspicuous 1. Sphaeelariales (p. 390) 



2. Terminal cell, if present, at least not conspicuous. .2. Ectocarpales (p. 398) 



3. Growth of zoosporangial frond, strictly terminal 5. Dictyosiphonales (p. 586) 



3. Growth of zoosporangial frond not strictly terminal 4 



4. Growth of zoosporangial frond trichothalHc 3. Desmarestiales (p. 554) 



4. Growth of zoosporangial frond not trichothalHc 5 



5. Growth apical, from subapical cells 4. Chordariales (p. 570) 



5. Growth never apical, either intermediate or near the base .. 6. Laminariales (p 590 ) 



Order 1. SPHACELARIALES oltmanns 



Filamentous, generally tufted and branched Phaeosporeae, rarely 

 monosiphonous throughout, usually monosiphonous near or at the tips, 

 becoming polysiphonous below through longitudinal walls, and in some 

 cases corticated slightly or considerably by descending filaments, 

 attached by horizontal rhizoids often cohering to form a disk, or, in 

 some cases, arising early and forming a more or less complex hori- 

 zontal thallus giving rise to the erect filaments ; growth of each erect 



