Tetranspora 



133 



associated with Anabsena in the water-bloom. Ccelos- 

 phserivun is a spherical hollow colony of microscopic size. 

 It is a loose association of cells, any of which on separa- 

 tion is capable of dividing and producing a new colony. 

 Microcystis (fig. 51^) is a mass of smaller cells, a very 

 loose colony that is at first more or less spherical but 

 later becomes irregularly lobed and branching. Such 

 old colonies are often large enough to be observed with 

 the naked eye. They are found most commonly in late 



summer, being hot 

 weather forms. When 

 abundant these two are 

 often tossed by the 

 waves upon rocks along 

 the water's edge, and 

 from them the dirty blue- 

 green deposit that is 

 popularly known as 

 "green paint." 



Among the members 

 of this group most com- 

 monly seen are the motile 

 blue-greens of the genus 

 Oscillatoria (fig. 51G). 

 These grow in dense, strongly colored tufts and patches 

 of exceedingly slender filaments attached to the bottoms 

 and sides of watering troughs, ditches and pools, 

 and on the beds of ponds however stagnant. They 

 thickly cover patches of the black mud bottom 

 and the formation of gases beneath them disrupts their 

 attachment and the broken flakes of bottom slime that 

 they hold together, rise to the surface and float there, 

 much to the hurt of the appearance of the water. 



The filaments of Oscillatoria and of a few of its near 

 aUies perform curious oscillating and gliding movements. 

 Detached filaments float freely in the open water, and 



Fig. 51. Miscellaneous blue-green 

 algse (mostly after West). 



A , Microcystis (Clathrocystis) ; 

 Tetrafedia; B. Spirulina; F, 

 Oscillatoria; H, Rivularia, 



B. C, 



Nostoc; 



