Ulothrix 145 



present, excepted) capable of division and of transformation into 

 sporangia. Each cell contains one band-shaped or reticular, or 

 one to several disk -shaped chromatophores. Vegetative repro- 

 duction by breaking apart of the cells to form new filaments. 

 Asexual reproduction by means of zoospores which germinate im- 

 mediately or after a period of rest, by akinetes, and by aplanos- 

 pores. Sexual reproduction through isogamous fertilization or 

 conjugation of gametes of similar size and character. 



Synopsis of Genera 



Filaments attached ; chromatophore a homogeneous, zonate band, with one to several 

 pyrenoids. I. Ulothrix. 



Filaments not attached ; chromatophore a parietal disk or plate, with one pyrenoid. 



II. Stichococcus. 



Filaments generally not attached ; chromatophore granular, covering more or less com- 

 pletely the whole cell wall, containing starch but no pyrenoids. 



III. MlCROSPORA. 



Filaments attached only when young ; chromataphores several, disk-shaped, without 

 starch. IV. Tribonema. 



With the exception of Ulothrix and Stichococcus the genera of 

 this family are not closely related. These two may be considered 

 as having a common origin from a unicellular form, or the former 

 may be derived from the latter. Microspore in its chromatophore 

 structure at least, shows some affinity with Rhizoclonium of the 

 Cladophoraceae, although it is always distinguished from the latter 

 by the absence of pyrenoids, and the single nucleus. 



Tribonema in all probability had a different origin and is appar- 

 ently more closely related to the Ophiocytiaceae than to the other 

 genera of the Ulothricaceae. 



I. ULOTHRIX Kiitzing, Flora, i6: .517-521. 1833 



Hormiscia Aresch. Act. Reg. Soc. Sci. Upsal. III. 6 1 : No. 

 2. p. 12. p. p. 1866. Not Fries, Flor. Scan. 327. 1835. 



Including Hormospora Breb. Ann. Sci. Nat. Bot. III. 1 : 25. 



1844. (?) 



Filaments consisting of a single series of uninucleate cells, all 

 (except the rhizoid-like basal cell) capable of division and repro- 

 duction. Chromatophore a homogeneous parietal band (some- 



