122 ILLINOIS BIOLOGICAL MONOGRAPHS [220 



EXPLANATION OF PLATE 



Fig. 39. Boneyard just below Urbana septic tank outlet. September 14, 1920. 



Fig. 40. Salt Fork canal west of Cottonwood's road bridge. Note bare sand bars with 

 stream meandering between. Bars are covered with green putrescent matter dried by the 

 sun. September 14, 1920. 



Fig. 41. Salt Fork canal at entrance of small ditch from Champaign outfall pipe. Note 

 sludge bank in foreground and sewage indicated by daxk color of water in center of picture. 

 September 14, 1920. 



