like chloroplast which shows significant similarity to that possessed 

 by the Volvocales and most Tetrasporales. Usually 1 or more pyre- 

 noids are present. In some forms there is a basal-distal diflFerentia- 

 tion, with an attaching holdfast cell. Most species which are attached 

 when young, however, become free-floating. Isogametes and zoo- 

 spores are produced in unspecialized vegetative cells. There are two 

 suborders. 



Suborder Ulotrichineae 



FAMILY ULOTRICHACEAE 



Nearly all the members of this family have cylindrical, uniseriately 

 arranged cells, either adjoined or separated from one another. In a 

 few forms there is a gelatinous sheath. The chloroplast is a parietal 

 plate or band which varies in the degree to which it encircles the 

 cell wall. In a few species a special holdfast cell develops at the 

 base of the filament, the only cell incapable of further division. Re- 

 production is by vegetative proliferation, by palmella stages, by 

 zoospores, and by isogametes. 



Key to the Genera 



1. Filaments tapering at one end, and ending in a stout blunt point — Uronema 



1. Filaments not tapering, the same diameter throughout 2 



2. Filaments inclosed by a gelatinous sheath _ 3 



2. Filaments not inclosed by a gelatinous sheath 7 



3. Cells cylindrical, adjoined at the end walls to form continuous filaments-— 4 



3. Cells oblong or spheroidal, sometimes not forming continuous threads 5 



4. Chloroplast a parietal band, nearly encircling the cell Ulothrix (in part) 



4. Chloroplast a parietal fold or plate, not encircling the cell, 



covering only a small portion of the wall Geminella (in part) 



5. Cells spheroidal, adjoined in some species with the wall composed of 

 2 helmet-shaped halves which adjoin 



in the midregion Radiofilum 



5. Cells of different shapes from those above; wall 



not composed of two halves - 6 



6. Cells cylindrical, frequently in linear pah's, forming filaments 



of indefinite length Geminella (in part) 



6. Cells transversely elliptic, in discontinuous series, often in groups of 4, 

 each group inclosed by a sheath; filaments short — Hormidiopsis 



7. Filaments with cells in pairs, the protoplasts at some 

 distance from the wall, the intervening space filled with 



lamellate gelatinous deposits Binuclearia 



7. Filaments with cells not in pairs and without gelatinous 



deposits about the protoplasts 8 



8. Filaments of indefinite length, composed of many cells, 



sometimes with basal differentiation 9 



[94] 



