THE LIFE OF DEVIDS LAKE 103 



comparison of their algae is impossible, but, in general, the alkalinity 

 appears to be a limiting factor in the distribution of these plants, 

 the higher the amount of alkalinity the smaller the number of 

 species. Big Alkali lake with 622 ppm. of "alkalinity'' is probably 

 most like Devils Lake, but as this was visited only once, only a very 

 superficial comparison of their algae is possible. Of 26 species re- 

 corded from this lake 16 occur in Devils Lake and every genus is 

 represented except Chara. 



Recently Moore and Carter (1924) have extended the survey 

 of the former (Moore, 1917) to include about 70 lakes in central 

 North Dakota, including both fresh and alkaline types. As a re- 

 sult of this study these authors conclude; "that as far as the Myxo- 

 phyceae are concerned the 'alkaline' lakes are considerably richer 

 in species than the 'freshwater' lakes. On the other hand a def- 

 inite 'bloom' was rarely developed in strongly alkaline waters, 

 whereas in several of the 'freshwater' lakes there was frequently 

 a copius 'bloom' consisting of Clathrocystis aeruginosa, or some- 

 times of Aphanizomenon flos-aquae, one or other of these species 

 being dominant, and often the only representative of the Myxophy- 

 ceae in the sample. In the alkaline lakes there was never such a 

 pronounced development of a single species of Oscillatoria, Nodu- 

 laria spumigena, Arthrospira Jenneri and Spinilina spp. The tiny 

 species Rhabdoderma sigmoidea, described here for the first time, 

 also occurred in some of the alkaline lakes as a dominant constituent. 



With regard to the Chlorophyceae, the condition is reversed. 

 Many of the species seem to be very intolerant of increasing con- 

 centration of salts, and are therefore eliminated from the flora of 

 the strongly alkaline lakes. On the whole the Conjugatae are very 

 poorly represented, as pointed out by Moore (I.e., p. 302), although 

 a few species are able to thrive under the unusual conditions. The 

 genus Oocystis seems to maintain itself satisfactorily in the alkaline 

 waters, as do also some species of Scenedesmus, Pediastrum, and 

 Dictyosphaerium spp. Many of the Protococcales commonly found 

 in freshwater plancton are not represented at all, however, in lakes 

 of the 'alkaline' group. 



The 'alkaline' lakes were conspicuous by reason of their paucity 

 of species, the richest lakes of this type containing only 5-9 species, 

 whilst some of the 'freshwater' lakes had as many as 12-17 species." 



While the number of species inhabiting Devils Lake is rather 

 restricted, especially in certain groups; the number of individuals 

 of a few species is large. This is especially noticeable in the case of 

 the rotifers Brachionus and Pedalia and in that of the Myxophy- 

 ceae, Nodularia and Coelosphaerium. It is quite possible that the 

 paucity of certain species, thereby restricting competition, has per- 

 mitted a greater development of others than would otherwise have 

 occurred. More important factors, however, are probably the favor- 



