PAPERS OX BIOLOGY AND AGRICULTURE 1S9 



The underlying soil is shale, above which is the forma- 

 tion of ooze of animal and vegetable debris. 



The water of the pond is comparatively clear so that 

 light can penetrate to the bottom. In the mnskrat region, 

 however, the water is more muddy in appearance but is 

 more shallow so that light can easily penetrate. The 

 winter was not severe but the lake was covered with ice 

 most of the time until the last of February. The first 

 killing frost was October 29th and the last frost, which 

 was a slight one, was April 23rd. 



Much of the wind is kept off by the surrounding hills 

 and by the banks which are three or four feet higher 

 than the surface of the water. Wind is an important fac- 

 tor in determining the circulation of the water which 

 affects living organisms. 



Chemical Conditions of Water. Water was taken 

 about three inches below the surface at a distance of 

 a few feet from the shore, on a slightly cloudy day. The 

 chemical tests were made by Professor J. E. Xeifert, 

 Department of Chemistry, Knox College. He found the 

 oxygen content very low, 5.2 parts per million by weight. 

 The hardness in CacOs units was 168 parts per million 

 and the alkalinity was 205 parts per million. 



The character of the margin (whether rocky or 

 swampy), that of the shore (whether steep or shal- 

 low), the outline (whether smooth or jagged), the 

 depth of the lake, the chemical content of the soil, the 

 banks, the exposure to sun and wind, relative inflow and 

 outflow in relation to volume, the altitude, and the geo- 

 graphic location — all these factors modify and control 

 the types of living things and their abundance in the 

 water. 



Lakes are only temporary; inflowing water brings 

 detritus which fills in the shore for a new kind of vege- 

 tation. This region increases as the lake advances in 

 age, and open water and bottom areas decrease likewise 

 till a SAvamp results which is gradually reduced to dry 

 land. 



Life in the lake changes as the lake changes. At first 

 there is little fauna, but it increases as new habitats are 

 formed. Raw materials are washed in and plants and 



