PROGRESS IN BIOLOGICAL. INQUIRIES 29 



acres and in maximum depth from 2 to 35 meters. During the sum- 

 mer of 1925 the surface temperature was as low as 19° C. in some 

 of these lakes and as high as 24° C. in others. 



These bodies of water may be regarded as having soft water, as 

 they hare only a relatively small amount of calcium and magnesium 

 in solution. Several, which have neither an inlet nor an outlet, con- 

 tain less than 2 cubic centimeters of fixed carbon dioxide per liter; 

 most of them have between 5 and 12 cubic centimeters per liter. 



The epilimnion, or upper stratum of water, in these lakes was well 

 supplied with dissolved oxygen, the amount ranging from 5 to 7 

 cubic centimeters per liter of water. In some of the deeper ones the 

 the hypolimnion, or low water, possessed very little or no dissolved 

 oxygen at all in late July and in August. 



In the lakes having a depth of 5 meters or more the lower water 

 generally yielded a larger amount of free ammonia than the upper 

 stratum; the reverse was true of some of the lakes that possessed a 

 relatively small amount of plankton. The quantity of free ammonia 

 found in the upper water of the various lakes varied from a minimum 

 of 0.024 to a maximum of 0.148 part per million; this represents a 

 sixfold difference. In the lower water the quantity of free ammonia 

 ranged from a minimum of 0.020 to a maximum of 0.968 part per 

 million. 



The theory has recently been advanced that the quantity of phyto- 

 plankton produced by a body of water is dependent upon the amount 

 of phosphorus that is available in the water. In order to see whether 

 such a correlation could be established for these lakes, a quantitative 

 study of the phosphorus was made, but the data obtained in 1925 do 

 not warrant any definite conclusions. It was found that the quantity 

 of phosphorus in the upper water ranged from none at all to a maxi- 

 mum of 0.095 milligram per liter of water. No phosphorus was 

 obtained in the lower water of one small lake that is only 7 meters 

 deep, but the lower water of all of the other lakes yielded a measur- 

 able amount of phosphorus. The quantity varied between 0.005 and 

 0.09 milligram per liter in most of the lakes. A maximum of 5 

 milligrams per liter was noted in a lakelet only 122 meters (400 feet) in 

 diameter, but which is 22 meters (72 feet) deep. 



The lowest readings for hydrogen-ion concentration were obtained 

 in 11 lakes that have less than 2 cubic centimeters of fixed carbon 

 dioxide per liter of water; in this group the reaction ranged from pH 

 6.9 at the surface to pH 5.4 at the bottom. It will be noted that all 

 of these readings were on the acid side. In the lakes that had more 

 than 2 cubic centimeters of fixed carbon dioxide per liter of water 

 the surface water was neutral or alkaline (pH 7.1 to 9.4), while the 

 bottom water of some of them was acid and of others neutral or alka- 

 line (p H 6.4 to 7.6). 



The total plankton varied from a minimum of 545 to a maximum 

 of 6,990 milligrams of dry organic matter per cubic meter of water. In 

 general, the shallower lakes yielded a larger amount of plankton per 

 cubic meter of water than the deeper ones. The maximum was 

 obtained from the surface water of a lake having a maximum depth 

 of only 8 meters. 



A few quantitative observations were made on the larger bottom- 

 dwelling animals, but only a very limited amount of time could be 

 spent on to this phase of the general investigation. An interesting 



