of the genus critically. Teiling (1946) advocates the retention of 

 the two names. 



If the interpretations of Elenkin (I.e.), Drouet and Daily (I.e.) 

 and others are followed, the name M. jios-aquae (Wittr. ) Kirch, 

 will be discarded. The view which holds that the clathrate condition 

 is a result of age only, is not compatible with the many observations 

 which I have made on collections of these forms in which very 

 large, globose, solid colonies dominate the habitat, forming almost 

 pure growths in some lakes. Such colonies mature and disintegrate 

 without assuming the perforate and clathrate condition which one 

 might expect to develop if age were responsible for the aeruginosa 

 form. Illustrations of some of the various expressions which this 

 plankter assumes are illustrated on Plate 102, Figs. 1-4. See also 

 Fjerdingstad ( 1945 ) on the retention of these two names. 



Microcystis incerta Lemmermann 1899a, p. 132 



[M.pulverea (Wood) Migula] 



PI. 102, Fig. 5 



A spherical or lobed colony, consisting usually of many small, 

 spherical, closely arranged cells, inclosed by a thin, mucilaginous 

 envelope; cells 0.5-2/x in diameter; cell contents gray-green to light 

 blue-green; pseudovacuoles lacking or minute and inconspicuous; 

 colonies either tychoplanktonic, or forming blue-green granular 

 masses on the bottom. 



Not uncommon, occurring in both hard and soft water lakes. 

 Mich., Wis. 



The small size and compact arrangement of the cells, and the 

 minute pseudovacuoles are characteristics which aid in the identi- 

 fication of this species. 



I follow Drouet and Daily (I.e.) in assigning forms ordinarily 

 hsted under the name of M. ptilverea (Wood) Migula to M. incerta 

 Lemm. The plant listed by other authors as Anacystis pulverea Wolle 

 has been transferred to M. glatica (Wolle) by Drouet and Daily 

 ( I.e. ) . Apparently it has not been collected in our region. It inhabits 

 hard water lakes rich in lime and is to be expected in lakes of 

 southern Michigan and Wisconsin. 



MERISMOPEDIA Meyen 1839, p. 67 

 A plate-like colony of ovate or globose cells compactly or loosely 

 arranged in rows both transversely and longitudinally, inclosed by 

 a hyaline, homogeneous, mucilage; colony quadrangular (becoming 

 distorted in age ) or with margins rolled and convolute; cell contents 

 homogeneous ( rarely with pseudovacuoles ) ; individual cell sheaths 



[457] 



