ii8 Roosevelt Wild Life Bulletin 



ascribe a dearth of these organisms to low temperatures. Lack of 

 nitrogenous compounds may be a factor since it is well known that 

 when waters are even slightly contaminated by drainage from a 

 settled area there is a very considerable increase in the blue-green 

 content of the plankton. 



Seasonal Succession of the Plankton Algae. This discussion 

 of the plankton constituents of the Park lakes may have suggested 

 that the flora is quite constant in lakes of the Caledonian type or 

 that the flora is constant from month to month. On the contrary 

 each lake of the Caledonian type has a distinctive flora, certain 

 species predominating in one lake and other species in another lake. 

 There is likewise a variation of the flora as the season progresses. 

 This seasonal variation of the flora has been noted by every investi- 

 gator who has followed the biological history of a lake for a year, 

 and the spring maximum of diatoms, sometimes followed by a second 

 autumnal maximum; an early summer maximum of Chlorophy- 

 ceae and a late summer and early fall maximum of Myxophyceae 

 are well known to all. These regular seasonal successions are found 

 in all parts of the world, although a lake in the southern hemisphere 

 would have midsummer conditions in February and March (G. S. 

 West, '09). Since the observ^ations on the Park lakes were carried 

 on from July i to September i the complete seasonal succession was 

 not observed, although the normal changes which were to be expected 

 at that time w^ere noted. In the case of the Caledonian plankton 

 formation these seasonal changes were not very pronounced, chiefly 

 because the blue-green algae did not increase at the end of the 

 summer, a fact to which Wesenberg-Lund ('05) and W. & G. S. 

 West ('05) have already called attention in their comments on 

 conditions in Scotch lakes. 



Algal Succession in Artificial Lakes. Although the natural 

 lakes of the Park region have the characteristic low plankton volume 

 and small blue-green content of the Caledonian community, the new 

 artificial lakes have a quite different flora, blue-green algae occurring 

 in sufficient quantity to be a troublesome pest. One of the primary 

 objects of the investigation of these lakes was to obtain light on 

 the problem of ecological succession in the plankton community of 

 artificial lakes, and to see if there is any reason for expecting 

 that artificial lakes will eventually reach the biological conditions 

 found in the natural lakes of the region. 



Miss Monti ( '06) seems to have ]:>een the only investigator to take 

 up this problem of ecological succession in a newly formed lake. 

 Her investigations were made on small alpine glacial lakes which 

 were about thirty-five years old when examined. The flora of these 

 lakes was rather poor, consisting chiefly of diatoms and a few 

 Protococcales. The Myxophyceae were not found at all, probably 

 on account of the temperatures of the water, which, even under mid- 

 summer conditions, did not exceed i to 11 degrees Centigrade. The 

 poverty of phytoplankton in these lakes makes it unsafe to draw 

 any general conclusions from her results. 



