59 
or 
our own, raises a doubt as to the value of any conclusions de- 
rivable from such data. Steuer (’01) has suggested that the 
geographical position of the bodies of wafer in a large measure 
determines the character of the planktograph. I should pre- 
fer rather to put the emphasis upon temperature, which is not 
everywhere merely a matter of latitude, and also to insist upon 
the dominance of purely local conditions over those more gener- 
ally operative, such, for example, as temperature, in determin- 
ing the amplitude of the movements of the planktograph and 
the general position of seasonal maxima. Illustrations in sup- 
port of this view can be found in our own records—for example, 
in Phelps and Quiver lakes. These are bodies of water within 
three miles of each other, and with quite similar temperatures, 
yet their planktographs are in some years quite as different as 
any of those whose difference Steuer seeks to explain by lati- 
tudinal positions. Furthermore, the ‘“Sommerschlaf” which 
he predicates as probable in tropical waters is least of all evi- 
dent in Phelps Lake, the warmest of all our localities, where 
temperatures during midsummer approximate those of the 
tropics. More chronological series of collections at brief in- 
tervals, not exceeding a fortnight, from many localities are 
needed before general conclusions of permanent value concern- 
ing the seasonal course of plankton production will be possible. 
The maximum production has been used by some writers as 
a basis of comparison of plankton production in different 
bodies of water. It doubtless has a slight value in suggesting 
the relative productivity of waters, though it would seem that 
an annual average of weekly or fortnightly collections would 
be very much more accurate. Difficulty attends these com- 
parisons when deep and shallow waters are brought into con- 
trast. If the volume of plankton under one square meter is 
made the basis the shallow waters are at a disadvantage, while 
if the amount per m.° is made the basis the more barren deeper 
strata reduce the average plankton content of deep waters to 
a relatively small figure. Since, however, all strata, at least of 
most bodies of fresh water, are productive of plankton, it 
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