186 Wisco7ism Academy of Sciences, Arts, and Letters. 



but our knowledge of the conditions of tlie water at those times 

 is very imperfect. There should be a systematic examination, 

 by chemical analysis, of the water and its contained gases, and 

 of the mud of the bottom, and an exact comparison should be 

 made between the lakes with sterile bottom waters and those with 

 comparatively abundant faima. In connection with this should 

 be a studv of the currents of the abvssal region. A more careful 

 and thorough examination should be made of those lakes whose 

 geological history indicates that they were formerly connected 

 with the sea, and may contain a ^^fauna relicta." I may say that 

 it is not likely that such explorations will yield any startling re- 

 sults. The time for that is probably past, and the lake student 

 of the future must content himself with hard work, without the 

 satisfaction of brilliant discoveries. 



Our quantitative knowledge of plankton is only a beginning. 

 We know something of the conditions on a few lakes, but only 

 on a few, and we do not know what variations may be caused by 

 the peculiarities of individual lakes. Even in the same lake the 

 conditions may change from year to year, and in only a few in- 

 stances have observations continued through a series of years. 

 We are all prone to generalize on the facts in our hands, but it 

 must be acknowledged that the facts upon which we can build 

 theories of fresh-water plankton are very meager. There is 

 need of a series of examinations of typical lakes carried on for 

 a term of vears, before we can build with certaintv. 



There remains the great problem, or complex of problems, 

 of the relation of the different elements of the plankton to each 

 other and to fish. We see, frequently, an apparent overproduc- 

 tion of one of the elements. In shallow lakes — at least in many 

 of them — there is apparently a great overproduction of vegeta- 

 tion. How is this explained ? How is the balance of life re- 

 stored ? What constitutes an ideal relation betw^een the vege- 

 table and animal growth ? When we plant a new species of fish 

 in a lake, we, of course, disturb the existing balance of organ- 

 isms ; may we not, in some cases, at least, work actual damage ? 

 To what extent is this balance betw'een animals and plants main- 

 tained in a lake that is not interfered with by man ? 



These and similar questions, now without answers, offer a 



