HOW TO KNOW THE FRESH-WATER ALGAE 



302a Filament branched. Fig. 211 MONOCIL1A 



Fig. 211. Monocilia viridis Gerneck. 



This and another species, M. flavescens 

 Gerneck, are the only ones reported from 

 this country, the former being more com- 

 mon. It occurs as an irregularly and in- 

 definitely branched filament in soil. A 

 member of the Chrysophyta, the disc-like 

 chromatophores are yellow-green or yel- 

 low in color, and the food reserve is in 

 the form of oil; starch test negative. 



Figure 21 1 



302b Filament not branched 303 



303a Cells long-cylindrical; wall of cells formed of 2 pieces which over- 

 lap at the midregion, the overlapping usually evident when empty 

 cells are viewed; filaments showing H-shaped pieces upon frag- 

 menting; cells often with lateral walls convex. Fig. 212 



TR1BONEMA 



-C <C? C 7 " 



Q_ 



-xy — c=» — c? o^ 



.O r>> r~^ — n nn , 



■x^ c? 



"C7- 



^3J2§§E 





Figure 212 



Fig. 212. a, Tribonema bombycinum var. fenue Hazen; b, T. bomby- 

 cinum (Ag.) Derbes & Solier; c, T. utriculosum (Kuetz.) Hazen. 



There are 3 or 4 species of this simple, unbranched filamentous 

 member of the Chrysophyta, differentiated by proportions of the cell 

 and number and shape of the chromatophores. Like Microspore! (Fig. 

 172) in the Chlorophyta, the cell walls are composed of 2 sections which 

 adjoin and overlap in the midregion of the cell. Hence when the fila- 

 ments fragment the typical H-shaped sections are seen. By careful 

 focusing the overlapping of the wall sections can be seen in the un- 

 fragmented portions of the filament, especially in some species which 

 have a relatively thick wall. The chromatophores are pale-green or 

 yellowish and occur as parietal discs. 



131 



