THE GREEN ALGAE OF NORTH AMERICA 181 



A family of fresh water and marine algae, fairly well marked 

 off from other forms by the characters just given ; but it is by 

 no means easy to determine by hasty inspection whether a plant 

 belongs to this family or to the Cladophoraccae . In external ap- 

 pearance and even by ordinary microscopic inspection, there 

 is no test to distinguish Ulothrix, Hormisda, or Chaetomorpha ; 

 only by actual acquaintance with the individual species can one 

 acquire any certainty of determination. 



In the arrangement of this family Hazen, 1902, has been fol- 

 lowed, except that Conferva has been removed. While there 

 may be some doubt as to the distinctness of all the species he 

 has accepted, and he himself expresses some such doubt, his 

 work represents the only careful and continued study that has 

 been made of the living plants in this country, and may well be 

 accepted until modified by later investigations. 



KEY TO THE GENERA OF ULOTRICHACEAE. 

 i. Filaments tnonosiphonous below, parenchymatous above. 



4. SCHIZOMERIS. 



i. Filaments monosiphonous throughout. 2. 



2. Cells loosely attached, in a wide, gelatinous sheath. 



3. RADIOFI^UM. 



2. Cells forming a cylindrical or moniliform filament, without ex- 

 ternal gelatinous sheath. 3. 

 3. Without pyrenoid. 6. MICROSPORA. 

 3. With one or more pyrenoids. 4. 

 4. Chromatophore a parietal disk or plate. 5. STICHOCOCCUS. 

 4. Chromatophore a zonate band, sometimes incomplete. 5. 

 5. Apical and basal cells attenuate. 2. URONEMA. 

 5. Apical and basal cells little if at all differentiated, i. UI.OTHRIX. 



i. ULOTHRIX Kiitzing, 1833, p. 517. 



Filaments of a single series of uninucleate cells, all similar, 

 and, with the exception of the attached basal cell, capable of 

 division and of producing spores. Chromatophore band-shaped, 

 with one or more pyrenoids. Asexual reproduction by aplano- 

 spores and akinetes, also by 4-ciliate zoospores, with red stigma, 

 formed 1-4 in a cell, germinating immediately; sexual repro- 

 duction by biciliate zoogametes formed 8 or more in a cell, 

 germinating after conjugation. External conditions may induce 

 many modifications of the normal process ; resting spores may be 

 formed, ultimately producing zoospores; filaments may break 

 up into individual cells, and these by copious formation of 

 gelatine pass into a Palmella or a Gloeocystis condition. 



