121 



TUAXSPAKKXC'Y. 



The transparency of the water was determined by means of a Seechi's 

 disk, about fifteen centimeters in diameter. The depth at which this disk 

 just disappeared from view varied from 2.1 meters as a minimum to 2.5 

 meters as a maximum. 



TEMPERATURES. 



The thermophoue and deep sea thermometer were not in working 

 order so that the temperatiu-es had to be taken by means of a pump and 

 hose. This method, of course, is subject to considerable error and the 

 results were found to be of comparatively little value except to determine 

 the location and extent of the thermocline, so that the distribution of the 

 plankton witli regard to this region, might lie studied. 



The temperature observations were made in the deepest part of the 

 lake, and they consisted of eight sets in July and ten sets in August. 

 During July there was very little wind so that tlie upper stratum of water 

 was not disturbed to any great extent. As a result this stratum accu- 

 mulated considerable heat during this period. The surface temperature, 

 taken at a deptli of eiglit or ten centimeters, averaged 28.0° C. for the 

 eight sets of observations, witli ol.2° C. as a maximum. 



During August, however, the Aviud was much stronger and the upper 

 stratum of water was mucli more thoroughly stirred up. As a result, the 

 average surface temperature for tlie ten sets of observations was 25.0° 

 with a maximum of 20.0.° 



Tlie tliermocline consisted of a stratum of water three meters in thick- 

 ness. The difference in temperature IjetAveen tlie top of this stratum and 

 the bottom of it varied between 0.0° and 12.0°. In July it extended 

 from four meters to seven meters, and in August from five meters to eight 

 meters. The downward movement was doubtless due to the stronger 

 winds prevailing in August. 



The change in liottom temperature during the two months was very 

 sliglit. 7.")° being the minimum and 8.0° tlie maximum. 



METHODS. 



Tlie plankton observations as Avell as the temperature oliservations 

 were made in the deepest part of the lake and by the pump method. An 

 ordinary pitcher pump, 1-inch garden hose, and a plankton net whose 



