80 



PLANKTON DISTBIBUTIOX IN REFERENCK TO THE EPILIMNION, THERMOCLINE. ANI) 



HYPOLIMNION. 



Seventy-four and six-tenths per cent, of the plankton inhabited the 

 epilimnion. The per cent, of the eleven forms studied quantitatively are : 

 Rotifera 87.4, Lynghya 80.7, Ceratium 88.6, Microcystis 76. 5, AnaMena 84.8, 

 Tribonema 64.3, Nanplii 60..5, Diaptomus 71.2, Fragilaria 76.7, Cyclops 38.8, 

 Cladocera 31.6. 



Seventy-three and three-tenths per cent, of the phytoplankton and 83.3 

 per cent, of the zooplankton inhabited the epilimnion. 



The thermocline contained 21.8 per cent, of the plankton of the lake. 

 The followiiig synopsis gives the per cent, of each of the ele\-eu forms: 

 Diaptomus 23.8, Frafjiluria 19.5, Cyclops 34.4, Cladocera 40.7, Tribonema 

 26.6, Nanplii 18.7, Microcystis 20.3. Anahaena 14.4. Ceratium 10.3. Lynybya 

 IS, Rotif<rii 1(»..S. or the /.ooiil.-mkton 12..". ]>v\- cciil.. ••uid of tlic jiliytoijlank- 

 lon 22.6 per cent, lived in the tlU'nnocliiic. 



The hypolhnnion contained 3.."» jier cenl. of the iilanktoii, 1..". per cciil. of 

 the zooplankton, and .'{.4 per cent, of the phytoplankton. The per cent, of 

 each form in the hypolinniion was: Cladocera 27.7. Cyclops 26.7. Frayilaria 

 3.5, Nanplii 20.8. IHnptoiniis 5. Anabaena .8, Tribonema 9.1. Microcystis 3.2, 

 Lyngbya 1.1, Rotifera 1.7, Ceratium 1.1. 



At 23 m. there were more forms ])or liter than at 20 m. This was prob- 

 jibly due to the presence of some dead orj;anisms that by the loss of activity 

 liad i^unk to the bottom. The end of the hose at 23 m. was very close to the 

 bottom. 



THE EFFECTS OF PHYSICAL FACTORS UPON DISTRTHUTION. 



The large per cent, of plankton in the epilimnion was due to the i)res- 

 ence of sunlight and plenty of food. In the iipi»«'r half (best liglited i>art) 

 of this stratum, there was sufficient carbon dioxide to permit rapid photo- 

 .syntbesis. Apstein ("96) found ligiit to be tlie most important factor in ex- 

 plaining the presence of fifty-six times as much plankton from 0-2 m. as in 

 the remainder of the water. That direct sunlight has a repelling effect upon 

 some plaidcton, was demonstrated by the fact that .■'>3 i»er cent, inhabited the 

 tJr.st two meters, while only 12 per cent, lived at the surface. /. c. in the sur- 

 lace meter. Other factors enter into the exi)lanation of the ])roiilic life in 

 the epilimnion. Many organisms were too heavy to sink into the cold 

 heavy waters of the thermocline. Juday in his work on the Wisconsin 



