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^ (Cyanophycecs 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 of in 

 filaments. Their chlorophyll is rather uniformly dis- 

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

 restriction to specialized chlorOplasts seen in the true' 

 green-algse) 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 algae 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 import- 

 ant 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 Anahcenas (fig. oo), and other blue- 

 greens that mtdtiply 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 

 CcelosphcBrium and Microcystis. Both th^se' are often 



