ULOTHRIX 311 
Ulothrix. — Ulothriz (Fig. 267) is one of the simpler forms of 
the group, and its filaments, an inch or two in length, form bright 
green fringes about stones and other objects in lakes, ponds, 
streams, and troughs. There is some differentiation within the 
filament, for the basal cell is modified into a holdfast by which 
the filament is attached to a support. The other cells are alike 
and each contains one nucleus and a large encircling chloroplast. 
Fic. 267. — Ulothrix zonata. A, portion of a filament, showing the hold- 
fast and a number of vegetative cells; B, portion of a filament, show- 
ing three cells containing gametes; C, a portion of a filament, showing 
gametes escaping at b, and zodspores formed at a and escaping at c; D, anew 
filament developing from a zodspore, the character of which is shown at z. 
At g gametes are shown fusing to form zygospores. At zy a zygospore, just 
after the fusion of the gametes and when fully mature, is shown. A zygo- 
spore which has germinated and produced four zodspores is shown at y. 
X 200-300. Redrawn with modification from Coulter and from Strasburger. 
The plant reproduces asexually by four-ciliate zoéspores, and 
sexually by two-ciliate isogametes. The zodspores are formed usu- 
ally two or more ina cell. They escape together from the mother 
cell enclosed in a membrane, but soon separate and after swim- 
ming about for a short time become attached to some object by 
the ciliated end and by growth and cell division become new 
filaments. Some cells produce gametes, which, besides having 
only two cilia, are much smaller and more numerous than z0- 
ospores. After escaping. the gametes fuse in pairs to form resting 
zygospores. Upon germination, the zygospore does not pro- 
