108 CLARK— ON WATER CONTENT 



IV. Preliminary Problem 

 Location 



The Michigan Biological Station is situated on the south side of 

 Douglas Lake, about twenty miles south of Mackinac Island, in the 

 northern part of the Southern Peninsula of Michigan. Immediately 

 surrounding the camp is a xerophytic association of aspens; a mile and 

 a half east of camp lies a bog, in which are found the same species of 

 aspen in hydrophytic habitat. 



The Problem 



The problem in this preliminary work was to determine the water 

 content in the leaves of Populus tremuloides and Populus grandidentata 

 under both typically xerophytic and hydrophytic conditions for both 

 clear and cloudy weather. The topic thus naturally resolved itself 

 into the following heads: 



1. Populus tremuloides = xerophytic = clear 



2. Populus tremuloides = xerophytic = cloudy. 



3. Populus tremuloides = hydrophytic = clear. 



4. Populus tremuloides = hydrophytic = cloudy. 



5. Populus grandidentata = xerophytic = clear. 



6. Populus grandidentata = xerophytic = cloudy. 



7. Populus grandidentata = hydrophytic = clear. 

 8; Populus grandidentata = hydrophytic = cloudy. 



Apparatus 

 The apparatus used was in all cases simple and unoriginal. It 

 consisted of 144 homeopathic vials with paper labels and tight-fitting 

 corks; chemical balances, accurate to .5 of 1%; a gas oven; a Clements' 

 photometer, loaded with Solio paper; and an egg-beater psychrometer, 

 fitted with wet and dry bulb Fahrenheit thermometers. 



Detailed Method 

 For purposes of curtailing the work, the first and fifth, second and 

 sixth, third and seventh, and fourth and eighth divisions of the problem 

 were carried through simultaneously. The work thus resolved itself 

 into four different experiments, readings for which were taken every 

 hour for 24 consecutive hours. As far as possible, leaves of apparently 

 the same size were selected from the same trees. Experiments for 

 similar conditions were not duplicated and because of weather changes, 

 readings for xerophytic cloudy conditions were got for 12 hours only. 



