HOW TO KNOW THE FRESH-WATER ALGAE 



234a Chloroplast a parietal band or ring which encircles the cell or 

 nearly so. Fig. 167 ULOTHRIX 



"Fig. 167. a, Ulothrix 

 zonata (W e b e r & 

 Mohr) Kuetz., with 

 ring-like chloroplast; 

 b, U. cylindricum 

 Presc; c. U. aequal- 

 is Kuetz. 





mrs^w^p^iw^m 



Species of this genus 

 vary greatly in size 

 and proportions of the 

 cells. Some are short- 

 Figure 167 er thon wide, others 



distinctly cylindrical. The most familiar species, and the largest is 

 U. zonata (Fig. 167a) which has a basal holdfast cell and chloroplasts 

 which completely encircle the cell wall. Others have a chloroplast 

 that forms two-thirds to three-fourths of a circle. Usually there are 

 1 or more conspicuous pyrenoids. Whereas most species occur in 

 standing water, U. zonata may be found in streams and usually in 

 rather cold habitats. 



234b Chloroplast a laminate plate lying over a small portion of the 

 wall and not encircling it. See Fig. 165 GEMINELLA 



235a (231) Filaments not showing a basal-distal differentiation. Fig. 

 168 HORMIDIUM 



Figure 168 



Fig. 168. Hormidium Klebsii G. M. Smitn. 



This genus includes several species of simple, unbranched fila- 

 ments of cylindrical cells which are characterized by having chloro- 

 plasts which extend only part way around the cell and which are only 

 about one-half the cell in length. 



235b Filaments with a basal holdfast, 



236 



107 



