558 
mer rise in August. No trace, however, of the phenomenon of 
recurrent volumetric pulses-so prominent in our fuller records 
—appears in his infrequent data. His statement, “Den ganzen 
Winter hindurch ist hier constant das Planktonvolumen unmess- 
bar gering” (italics are his) has no counterpart in winter pro- 
duction in our backwaters. 
The plankton of the Elbe and its backwaters has been in- 
vestigated by Schorler (’00), but no volumetric determinations 
were made of its channel plankton because of the difficulties 
occasioned by the current and by detritus in suspension. The 
quantity of plankton per m.* in three of the backwaters was de- 
termined in twelve instances in April-October. There are in 
the data suggestions of a May-June maximum and of one in 
August, and the quantities are generally higher than the aver- 
ages in our backwaters, though the greatest amount, 146 cm.’ 
per m.*, falls below the highest of our records. The channel 
plankton of the Elbe was found generally to contain fewer 
species and individuals than its contiguous backwaters. 
The plankton of the Oder has been examined by Zimmer 
and Schréder (’99), but no volumetric determinations were 
made. Regarding the quantitative conditions, Zimmer makes 
the general statement that these are influenced by tempera- 
ture. The quantity in December—February is very small, rises 
in March, and again, to a greater degree, in May, but attains 
the maximum for the year in August, declining rapidly after 
the middle of September, and reaching the winter minimum in 
December. 
A comparison of the seasonal course of production of 
plankton in the various lakes that have been explored in re- 
cent years, with those of our several stations, does not promise 
any profitable results, since most of the quantitative work is 
limited in seasons, or has been made at such long intervals as 
—in the light of our results—to raise some question as to the 
representative value of such collections for comparison. In 
addition to this, the very great divergence in the annual plank- 
tographs of such localities as have been examined, including 
