253 
QUANTITATIVE INVESTIGATION OF THE PLANKTON. 
GENERAL CONSIDERATIONS. 
The purpose of this investigation was the determination, 
by measurement, of the quantity of minute organisms develop- 
ing in the water at intervals throughout the year, and by this 
means to trace the seasonal fluctuations in production, and 
the relation of quantitative changes to constant and fluctuat- 
ing factors of the environment, to flood and drouth, to chemi- 
cal conditions, to the ice blockade, and to vegetation; and to 
contrast production in waters of the main and tributary 
streams, in impounding backwaters and the channel, and in 
bottom-land lakes and the main stream. 
METHOD OF COLLECTION. 
The method used in determining the quantity of plankton 
was based upon that devised by Hensen (’87) and moditied by 
Apstein (’96) for use in fresh water. The changes and modifi- 
cations which were made to adapt the method to use in our 
situation and to correct some of its errors have been described 
in detail by me elsewhere (97); I shall, therefore, only briefly 
refer to a few phases of the subject of special pertinence or 
interest in this connection. 
The changes in method during the progress of the work 
are indicated in Tables II]-IX. From June, 1594, to May 20, 
1896, the plankton was collected by means of the silk net, 
made after Apstein’s smaller model (see Apstein °96) of No. 
20 silk bolting-cloth of Keller’s manufacture. This net was 
drawn through the water at a uniform rate of one half meter 
per second for a distance of thirty meters. As shown in the 
tables referred to, most of the hauls were made by the ob- 
lique-haul method devised by Prof. Frank Smith, in which the 
net was drawn along an oblique rope from bottom to surface 
across channel in the river, and across the current, where cur- 
rent existed, at our other stations of collection, except in 
