883 



dences of the destructive work of the carp are seen in their ac- 

 tivity in uprooting great patches of Sagittaria. Such condi- 

 tions were prevalent shortly after the August flood of 1896 (PI. 

 XXXI1L), when the combined action of the change in levels 

 and the invasion of fish destroyed not a little of the vegetation. 



COLLECTIONS. 



Systematic examination of the plankton in this area was 

 begun Oct. 17, 1895, and continued until Aug. 16, 1897. Six 

 summer collections were made in 1898 for the purpose of de- 

 tecting T) 'och ospli (v> -a . 



Owing to the surroundings of this region access to it ex- 

 cept during high water was a matter of much time and con- 

 siderable difficulty. Absence of roads and bridges made ap- 

 proach by conveyance impracticable, and save at maximum 

 overflow the elevation of the surrounding bottoms or the abun- 

 dant vegetation prevented the entrance of the steam launch- 

 The drift in the slough (PI. II.) and the matted, and in many 

 places impenetrable, growth of Scirpus fliiviatilis rendered ac- 

 cess to the small areas of open water an arduous task. At low 

 stages the only means of obtaining a collection was to wade 

 out through the morass to a suitable place. The difficulties of 

 approach in winter were even greater, when ice and the emer- 

 gent vegetation combined to interfere with rapid transit of any 

 considerable load. For these reasons this station, though one of 

 much local biological interest, was early dropped from our list. 



These same difficulties have enforced some variation in 

 the methods of collection (Table VII.) and in the locality at 

 which collections were made. In the autumn of 1895 they 

 were made by dipping water in scattered areas in the vege- 

 tation and in advance of the roiling of the water caused by 

 wading. On Feb. 28, 1896, a measured quantity of water from 

 successive levels was taken amid the standing but submerged 

 vegetation with a pump. Other collections prior to May 23, 

 1895, were made by the oblique-haul method and thereafter by 

 the plankton pump. 



