HOW TO KNOW THE FRESH-WATER ALGAE 



163a (158) Cells round. Fig. 119 TROCH1SC1A 



Fig. 119. a, Trochiscia gronulata (Reinsch) 

 Hansg.; b, T. obtusa (Reinsch) Hansg.; 

 c, T. reticularis (Reinsch) Hansg. 

 There are 5 or 6 species of this genus, 

 all solitary cells, which may be differ- 

 entiated by the type of wall decoration. 

 It is a little-understood genus and some 

 of the described species are doubtless the 

 zygospores of other algae. Some may be 

 the encysted or resting stages of still 

 other forms. In making identification of 

 plants with the outward characteristics of Trochiscia care should be 

 used in identifying the several disc-like chloroplasts which this genus 

 possesses. 



163b Cells oval. Fig. 120 BOHLINIA 



Fig. 120. Bohlinia echidna (Bohlin) 

 Lemm. 



This rather unique species (the 

 only one in the genus) appears in 

 i amorphous gelatinous masses. Re- 

 production is by internal cell divi- 

 sion to form autospores. Although 

 older cells are characteristically 

 spiny recently formed individuals 

 may be smooth-walled. The ob- 

 server should examine the plant mass for remains of the old cell walls 

 which will show evidence of the spinescence. 



Figure 120 



164a (157) Cells associated with fungi to form thalli of lichens. Fig. 

 121 TREBOUXIA 



Fig. 121. Trebouxia Cladoniae (Chod.) G. M. Smith. 



This species is an inhabitor of lichens and appar- 

 ently occurs nowhere else. The cells are spherical 

 and contain an axial rather than a parietal chloro- 

 plast like most of the other members of the Chlorococ- 

 cales. 



Figure 121 



164b Cells not associated with fungi in lichens 165 



165a Chloroplast 1, central, with radiating lobes extending to the wall 



166 



80 



