34 



were intermediate, and those from the general aspen area had 

 the highest water content. The averages of percentage water 

 content as obtained from the various collections were as fol- 

 lows: bog situation — 112, 126; dry aspen — 121, 134; and gen- 

 eral aspen — 142, 154. In each case the first figure given refers 

 to leaves from the upper portion of the tree, and the second 

 figure to the lower leaves. 



The idea that trees in bog situations are as unfavorably 

 located in regard to the availability of water as are trees in a 

 dry situation, is supported by data indicating the much lower 

 water content for the leaves of the bog trees than for those 

 from the dry aspen area, in spite of the fact that transpiration 

 must be much less in the bog situation. 



The fact that the trees of the general aspen area should have 

 a higher water content than those of the much drier aspen ridge, 

 shows the correlation between the availability of water and the 

 water content, as the situations are comparable in soil and in 

 plant association, with the amount of water in the soil and the 

 transpiration rate as the only variable factors. 



The data also indicate that upper leaves of Acer ruhrum 

 contain significantly less water than the lower leaves of the same 

 trees. A certain amount of correlation of the amount of water 

 present in the leaf with the general weather conditions is shown 

 by the fact that leaves collected after a prolonged period of hot, 

 dry weather had a water content markedly lower than that of 

 leaves collected only a few days after good rains. The lowest 

 percentage of water found in leaves, 107%, was in the upper 

 leaves of the bog trees on August 8, and the highest, 165%, in 

 the lower leaves of the general aspen habitat on July 3. 



Summary 

 An investigation of the water content of upper and lower 

 leaves of Acer ruhrum from different habitats on northern lower 

 Michigan during the summer of 1935 showed that at the driest 

 time of the day upper leaves normally had less water than lower 

 leaves (126: 140) and that leaves of trees in bogs had less water 

 in them than trees on dry ridges, and these in turn less than trees 

 in the general mesophytic aspen association (119:128:148). 



University of Michigan 

 Ann Arbor, Michigan 



