IVol. 10 



394 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



from which specimens have been received is about 30 in both 

 groups. There were only 11 lakes of the "intermediate" group, 

 and it was felt that the species observed in these would scarcely 

 give a representative flora for comparison with those of the more 

 numerous "alkaline" and "freshwater" lakes. The "intermedi- 

 ate " group has therefore been omitted from this comparative list. 



From a consideration of the list it is apparent that as far as 

 the Myxophyceae are concerned the "alkaline" lakes are consid- 

 erably richer in species than the "freshwater" lakes. On the 

 other hand, a definite "bloom" was rarely developed in strongly 

 alkaline waters, whereas in several of the "freshwater" lakes 

 there was frequently a copious "bloom" consisting of Clath- 

 rocystis aeruginosa, or sometimes of A phanizomenon flos-aquae, 

 one or other of these species being dominant and often the only 

 representative of the Myxophyceae in the sample. In the alkaline 

 lakes there was never such a pronounced development of a single 

 species to form a "bloom," and the Myxophyceae were usually 

 represented by various species of scillatoria , Nodularia spumi- 

 gena, Arthrospira Jenneri, and Spirulina 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 

 concentration 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 ('17, loc. 

 city p. 302), although a few species are able to thrive under the 

 unusual conditions. The genus Oocyslis 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 plankton are 

 not represented at all, however, in lakes of the "alkaline" group. 



The "alkaline 



by reason of their 



the richest lakes of this 



■v ^^ ^» ■- 



5-9 species, whilst some of the "freshwater" lakes had as many 

 as 12-17 species. Odessa Pond, I, and Strawberry Lake were 

 amongst the richest of the latter group, and Lake P and Coe 

 Lake were the richest of the "alkaline" group. 



