HOW TO KNOW THE FRESH-WATER ALGAE 



291a Chromatophores pale yellow-green with xanthophyll predominat- 

 ing; iodine test for starch negative; cell contents often showing 

 a metallic lustre. Phylum Chrysophyta. (This group of algae is 

 often difficult of determination on the basis of color of the chroma- 

 tophore alone inasmuch as the shades of green cannot be clearly 

 distinguished from those of the Chlorophyta. In addition to the 

 iodine test for starch (which ordinarily is confirmative) heating 

 plants in concentrated sulphuric acid (when the specimens lend 

 themselves to such treatment) provides a helpful differentiation. 

 The yellow-green algae (Heterokontae or Xanthophyceae) become 

 blue-green in the acid whereas Chlorophyta remain unchanged 

 in color) 300 



291b Chromatophores not yellow-green. 



292 



292a Cells with blue protoplasts or chromatophores 



293 



292b Cells with protoplasts or chromatophores not blue 



295 



293a One to four spherical or oval cells in a mucilaginous sheath which 

 bears a gelatinous bristle. Fig. 206 GLOEOCHAETE 



Fig. 206. Gloeochaete Wit- 

 tiockiana Lag. 



Figure 206 



This 



is 



an anomalous 

 organism, the morpholo- 

 gy and physiology of 

 which is interpreted as 

 one of symbiotism involv- 

 ing a colorless member 

 of the Tetraspora family 

 (Figs. 35, 48) and a blue- 

 green or cyanophyceous 

 endophyte. The proto- 

 plast is a parietal cup 

 similar to the chloroplast 

 of many of the green al- 

 gae. The long, slender gelatinous hairs make this species easy of 

 identification. Cells occur in clumps (rarely solitary) attached to fila- 

 mentous algae. 



293b Plants not as above; sheaths present or absent although cells may 

 be inclosed by old mother cell wall 294 



128 



