52 PLANKTON OF WINNE3AGO AND QREEN LAKES. 



gether in swarms, but I did not attempt to explain the reason of 

 the existence of swarms. I also stated my belief that single 

 plankton collections might give erroneous impressions, and 

 that an accurate measure of plankton could only be obtained by 

 averaging a considerable number of collections. 



Reighard (Reighard ? 98) acknowledges the uniformity of 

 distribution of the individual constituents of the plankton. 

 Yung (Yung '99 ), as the result of his studies on the plankton 

 of Lake Leman, states positively that the horizontal distribution 

 varies within wide limits and that there is no doubt of the ex- 

 istence of aggregations of organisms in certain localities. The 

 causes of these aggregations he states are diverse, but intimates 

 that sometimes currents may accomplish this. 



Steuer (Steuer '01) states that in his opinion there is no 

 further call for discussion, but that it must be admitted that 

 under similar physical conditions the^o will be uniformity in 

 horizontal distribution. He does not, nowever, give the reasons 

 for this opinion. 



While I felt quite sure that my position on the question was y 

 in the main, correct, it seemed to me desirable to make a con- 

 siderable number of collections to test the correctness of my 

 statement in a somewhat conclusive way. 



Two questions presented themselves for solution. First, the 

 comparative amounts of the plankton at different parts of the 

 lake at any given time. Second, if it was proved that there 

 was a difference in horizontal distribution, is this a fairly con- 

 stant difference between any two localities, or is it one that may 

 vary from day to day or from hour to hour ? 



To answer the first question, at several times collections were 

 made at a considerable number of locations on the same day. 

 The following table will show the results. In preparing this 

 table, I have listed no collections where less than four locations 

 were tested. In most cases the figures for the plankton were 

 tiie average of three collections. 



Erratum: Page 52, line 6, for " uniformity" read 

 " irregularity." 



