HOW TO KNOW THE FRESH-WATER ALGAE 



63a Cells arranged in groups of 4's at the ends of branching mucila- 

 ginous strands (focus carefully into the colony). See Fig. 52 .... 64 



63b Cells not arranged at the ends of branching strands 65 



64a Cells appearing both reniform (sausage-shaped) and ovoid in the 

 came colony. Fig. 52 D1MORPHOCOCCUS 



Fig. 52. Dimorphococcus lunatus A. Braun. 



In this plant the cells are in clusters of 4, 2 of 

 which when seen in 'top' view appear oval, 

 whereas the others, seen from the side, appear 

 bean-shaped or somewhat crescent - shaped, 

 hence the species name. Dimorphococcus luna- 

 tus is often abundant in soft water lakes, where- 

 as the other species known from this country, 

 D. cordatus Wolle, is less frequently found. 

 Both species may occur in open water plankton 

 or in the tychoplankton near shore. A char- 

 acter that is helpful in identification is a negative one, the absence of a 

 conspicuous gelatinous sheath inclosing the colony. 



Figure 52 



64b Cells spherical or broadly oval, all the same shape within the 

 colony. Fig. 53 D1CTYOSPHAERIUM 



Fig. 53. Dictyosphaerium pulchel- 

 lum Wood, a, Habit of colony; 

 b, Individual cells at ends of 

 radiating strands. 



Cells are in clusters of 4, as in 

 Dimorphococcus (Fig. 52) but all 

 the same shape, round or oval, 

 smaller in size and often more 

 numerous in the colony which is 

 invested by a colonial mucilage. 

 The radiating, branched thread- 



Figure 53 



like strands are the remains of the old mother-cell wall which has 

 broken down to release daughter-cells. 



65a Cells globular 66 



65b Cells other shapes, ovoid, fusiform, crescent-shaped, or bean- 

 shaped 68 



47 



