trichomes radiating from a common center; trichomes tapering from 

 a basal heterocyst to a fine hair-like point extending beyond the 

 limits of the colonial mucilage and so giving a burr-like appearance; 

 cells spherical or barrel-shaped at the base of the trichome, 8-10/x 

 in diameter, becoming long and cylindrical in the distal portion; 

 cell contents with many pseudovacuoles; heterocysts spherical, lOfi 

 in diameter; gonidia cylindrical, 10-1 8/^ in diameter, up to 50/t long, 

 adjacent to the heterocyst; sheaths colorless, wide, without lamella- 

 tions, covering approximately the lower third of the trichome. 



The colonies are macroscopic and appear as minute, dark, egg- 

 like or burr-like bodies, opaque in the center and translucent at 

 the periphery. The planktonic habit is associated with the pseudo- 

 vacuoles, which are often numerous and large. As is well-known, 

 those blue-green species which have a high degree of vacuolization 

 show a great buoyancy, often floating at the very surface. Gloeo- 

 irichia echiniilata, like Aphanizomenon fios-aquae and Microcystis 

 aeruginosa, often forms a dense suspension of thalli in upper lake 

 levels. Such superabundant growths are frequently followed by 

 unbalanced biological conditions as a result of the death and decay 

 of plant masses. During mid-summer and throughout the warm 

 season Gloeotrichia echiniilata makes periodic blooms, sometimes 

 becoming concentrated near the shore line and in shallow bays in 

 such numbers as to form a veritable puree. 



This species undoubtedly begins its life cycle in a sedentary or 

 attached condition, developing from gonidia of the previous genera- 

 tion. The mechanics involved in the germination which determines 

 the filament arrangement, the soft consistency of the colonial muci- 

 lage, and the volume of the cell contents occupied by pseudovacuoles 

 no doubt are responsible for the ready adoption of the planktonic 

 habit. Hence conspicuous growths make a sudden appearance in 

 lake plankton when large numbers of colonies become free-floating. 

 Wind and water currents and probably a change in physiology also 

 act to bring about a scattering and vertical distribution so that a 

 dense surface bloom may disappear as quickly as it developed. 



Common in the plankton of many lakes, especially in hard water 

 habitats. Mich., Wis. 



PGloeotrichia longiarticulata G. S. West 1907, p. 183 



PI. 134, Figs. 3-5 



Thallus hemispherical and attached, containing relatively few, 



widely separated, and loosely arranged trichomes which taper to 



a very fine point; sheaths confluent with the colonial mucilage; cells 



elongate-cylindric with rounded ends, (4.5)-9.5ju, in diameter, 3-7 



[558] 



