272 



suits in large part, doubtless, from the greater number of 

 catches averaged, and from the fact that they represent a num- 

 ber of more widely separated points in a larger body of water, 



DISTRIBUTION OF PLANKTON IN LAKE ST. CLAIR. 







Plankton per sq. m. of surface 



Plankton per m. 3 of water 



Haul 



No. 



Depth in 

 meters 











Volume in 



Departure from 



Volume in 



Departure from 







cm. 3 



mean in per ct. 



cm. 3 



mean in per ct. 



IlQ 



5.00 



7.19 



-29.4 



1.44 



-55-4 



II 



5.00 



I3.38 



+31-3 



2.68 



— 17.0 



IIIQ 



5-54 



15.27 



+49-9 



2.76 



— 14.6 



III 



5-54 



21.55 



+111.5 



3.89 



+20.4 



IVq 



2.50 



5.02 



-So. 7 



2.01 



-37-8 



IV 



2.50 



5.02 



-50.7 



2.01 



-37-8 



VQ 



5.26 



14.40 



+41.2 



2.74 



-15.2 



V 



5.26 



19.04 



+86.8 



3.62 



+ 12.1 



VlQ 



4.70 



10.93 



+7.2 



2.29 



— 29.1 



VI 



4.70 



14.69 



+44.2 



3.08 



-4-7 



VIlQ 



1. 17 



4-32 



-57-5 



3-69 



+ 14.2 



VII 



1. 17 



4-3 2 



— 57-5 



3-69 



+ 14.2 



VIIIQ 



4-44 



11.99 



+17.1 



2.70 



— 16.4 



VIII 



4-44 



13-36 



+31- 1 



3.01 



-6.8 



IXq 



4.28 



10.88 



+6.8 



2.54 



-21.3 



IX 



4.28 



10.22 



+0.3 



2-39 



—26.0 



Xq 



1.50 



6.23 



-38.8 



4.15 



+28.5 



X 



1.50 



6.23 



-38.8 



4.15 



+28.5 



XIIIQ 



2.21 



10.59 



+3-9 



4-79 



+48.3 



XIII 



2.21 



8.76 



— 14.0 



3-97 



+22.9 



XIVQ 



2.89 



10.41 



+2.2 



3.60 



+ 11.4 



XIV 



2.89 



9.56 



-6.2 



3-3' 



+2.5 



XVQ 



5-i7 



9.29 



-8.8 



1.80 



-44-2 



XV 



5-i7 



12.50 



+22.6 



2.42 



-25.1 



XVIQ 



4-55 



8.65 



-15. 1 



1.90 



—41 .2 



XVI 



4-55 



10.61 



+4.1 



2-33 



-27.8 



XVIIIQ 



1.27 



7.09 



-3°-4 



5.50 



+72.8 



XVIIlQ a 



1.27 



6.13 



-39-8 



4.83 



+49-5 



XVIII 



1.27 



7.85 



— 22.9 



6.18 



+91-3 



Av. 





10. 19 



±3i-8 



3-23 



±28.8 



Range 







+ 111.510-57.5 





+91.310-55.4 



in which currents, vegetation, shore, and bottom are important 

 factors environing its plankton. 



This large variation in the distribution of the plankton in 

 lakes naturally raises the question whether there is in the 

 channel of a running stream, for example the Illinois River, a 

 plankton whose uniformity of distribution is such that a collec- 

 tion made at a given place and time may be considered as a fair 



