132 Aquatic Organisms 



and loose ropy masses of gelatin of considerable size. 

 These masses are often large enough to be recognized 

 with the unaided eye as they lie outspread or hang down 

 upon trash on the shores of shoal and stagnant waters. 

 Within the gelatin are minute spherical bright green 

 cells, scattered or arranged in groups of fours. 



Blue-Green Alg^ {Cyanophycece or Myxophycece) . 

 The ''blue-greens" are mainly freshwater algae, of simple 

 forms. The cells exist singly, or embedded together in 

 loose gelatinous envelope or adhere in fiat rafts or in 

 filaments. Their chlorophyl is rather uniformly dis- 

 tributed over the outer part of the cell (quite lacking the 

 restriction to specialized chloroplasts seen in the true 

 green-algae) and its color is much modified by the 

 presence of pigment (phycocyanin) , which gives to the 

 cell usually a pronounced bluish-green, sometimes, a 

 reddish color. 



Blue-green algse exist wherever there is even a little 

 transient moisture — on tree trunks, on the soil, in 

 lichens, etc. ; and in all fresh water they play an impor- 

 tant role, for they are fitted to all sorts of aquatic 

 situations, and they are possessed of enormous reproduc- 

 tive capacity. Among the most abundant plants in the 

 water world are the Afiabcenas (fig. 179), and other blue- 

 greens that multiply and fill the waters of our lakes in 

 midsummer, and break in ' 'water-bloom" covering the 

 entire surface and drifting with high winds in windrows 

 on shore. Such forms by their decay often give to the 

 water of reservoirs disagreeable odors and bad flavors, 

 and so they are counted noxious to water supplies. 



There are many common blue-greens, and here we 

 have space to mention but a few of the more common 

 forms. Two of the loosely colonial forms composed of 

 spherical cells held together in masses of mucus are 

 Cwlosphcerium and Microcystis. Both these are often 



