WATER UTILIZATION BY TREES 77 



According to this early study, the common economic forest species 

 formed the following series: 



Water loss in per- 

 cent of fresh 

 Species: weight 



Black alder 43 



Oak 37 



Beech 36 



Birch 29 



Larch 18 



Fir 12 



Pine 11 



Spruce 10 



Hartig (88) measured the loss in weight at regular intervals of potted 

 plants in full foliage, 6 to 8 m high, placed in hermetically closed 

 vessels, calculating the transpiration loss in grams per square meter. 

 He found that, based on transpiration loss per unit area, alder topped 

 the list, heading the following series: Alder>hornbeam>pine>birch 

 >larch>aspen, beech, oak>spruce. 



In a later series of experiments (90) he found the amount lost in 

 grams per square meter of leaf area was as follows: 



Grams 



Black alder 1, 250 



Hornbeam 290 



Pine 255 



Birch 217 



Larch 206 



Aspen 155 



Beech 138 



Oak 136 



Spruce 106 



The principal objection to this work is that normal functioning of the 

 roots can hardly be expected in hermetically sealed vessels. 



Sorauer (198) studied the transpiration of maple, willow, basswood, 

 and pine during 74 days; and Ebermayer, deducing the water loss 

 from the ash content of the leaves, derived the four following groups: 



1. Ash content 7 to 10 percent: 



Ash, black alder, maple, elm, poplar. 



2. Ash content 4 to 5 percent: 



Beech, oak, hornbeam. 



3. Ash content 2.5 to 3.5 percent: 



Larch, fir, spruce. 



4. Ash content 1 to 2 percent: 



Pine. 



The objection to these latter figures, is of course, the assumption 

 that the ash content varies with the transpiration. While plants 

 that transpire more, probably have a higher ash content, the relation 

 is doubtless not a direct one. 



Still another method used by Ebermayer was the determination 

 of the water content of the leaves. In this experiment he obtained 

 the following results (in percent): Poplar, 70; ash, 66; alder and 

 locust, 64; oak, elm, and linden, 63; birch and Norway maple, 62; 

 aspen, beech, hornbeam, and field maple, 57. This method is so 

 unreliable that it was not even considered in the outline given above; 

 as far as one can tell there is no (or little) relation between the water 

 content of the leaves and the water requirements of the plant. Black 

 locust, for example, has a moderately high water content in the 

 leaves but can thrive on relatively dry soil. 



Of all the early workers on this subject, Von Hohnel (98, 99) has 

 impressed himself most upon the literature. He used potted trees 



