HOW TO KNOW THE FRESH- WATER ALGAE 



145b Cells elongate-ellipsoid or ovoid to subcylindrical; 1 parietal chlo- 

 roplast; cell contents violet-colored. See Fig. 46 . . MESOTAENIUM 



146a (126) Cells constricted in the midregion 147 



146b Cells not constricted in the midregion 154 



147a Cells flat, nearly circular in proportions, star-like in front view, 

 the median incision very deep; semicells deeply lobed or in- 

 cised, in some species forming secondary lobes and lobules. 

 Fig. 110 MICRASTEMAS 



Fig. 110. a, Micrasteiias americana var.; 

 Boldtii Gutw.; b, M. radiata Hass. var.; 

 c, M. ioliacea Bailey. 



These are true desmids and include some 

 of the most beautiful microscopic objects. 

 Although the outline of the cell varies 

 greatly among the twenty or more species 

 in this country, they can be identified by 

 the flat, disc-like shape. One species, M. 

 ioliacea Bailey, has hooks on the polar 

 lobes which enmesh with those of adjoin- 

 ing, newly-formed cells so that false "fila- 

 ments" are produced. 



Figure 1 10 

 147b Cells not flat and disc-like 



148 



74 



