WATER UTILIZATION BY TREKS 



25 



weighed potted seedlings, ranging in size from 2 to 25 ounces, of 

 various conifers and hardwoods, recording at the same time the daily 

 temperature and the humidity. Since the evaporation rates were not 

 compared with the leaf surface or weight, these results have little 

 quantitative value, but even a casual glance at his numerous tables 

 shows the increased evaporation of the hardwood species as compared 

 with conifers. 3 



According to Hartig (90) the transpiration per unit area in the 

 alder, beech, birch, oak, and aspen is to that of pine, larch, and 

 spruce on the average as 2.5 is to 1. Vogel (221) found the transpira- 

 tion ratio of beech in small trees taken from the forest and planted in 

 a flask containing some of the original forest soil was to that of spruce 

 as 5 is to 4, measuring the evaporation by loss in weight. 



Von Hohnel (100), in order to study this question, cultivated in 

 pots small (5- to 6-year-old) trees of Acer, Betula, Fagus, Quercus, 

 Tilia, Ulmus, Abies pectinata DC, Picea excelsa Link, Pinus laricio 

 Poir., and P. sylvestris L. Each pot was placed in a galvanized 

 cylinder and the soil was well protected from the air; 36 plants were 

 put under a shed and 30 in the open. The plants were weighed daily, 

 morning and evening, from May 27 to December 21, and the tem- 

 perature and humidity were recorded. In general the broad-leaved 

 trees transpired 8 to 10 times as much during the summer months as 

 the conifers. The next summer the experiment was repeated with 

 about 100 trees from April 1 to October 15 in the open and from then 

 on to the first of the following March indoors. Because of the 

 higher temperature and the decreased precipitation, the broad-leaved 

 trees this time transpired only about six times as much as the conifers. 

 From these two sets of experiments, one may conclude, therefore, 

 that under favorable conditions seedling broad-leaved trees will 

 transpire about eight times as much as conifers. 



Morosov (159, p. 113) calls attention, however, to the errors in the 

 work of Von Hohnel and points out that 8 to 12 pounds of earth was 

 much too little for trees 5 to 7 years old, and that the hermetical seal 

 was bound to result in some degree of root suffocation, to which he 

 attributes the high mortality of the seedlings. Possibly, also, the 

 internal temperature of the zinc pots was too high. Furthermore, 

 Von Hohnel calculated the amount of transpiration as based only on 

 the weight of the leaves, without taking into account the increment of 

 the stem and roots. 



Kusano (131) compared the winter transpiration of conifers (Cha- 

 maecyparis, Cryptomeria, Torreya, and Pinus thunbergii Pari.) in 

 Japan with that of broad-leaved evergreens (Quercus glaitca Thunb., 

 Eriobotrya, etc.). The average transpiration loss in percentage of 

 fresh weight and of dry substance is shown in table 6. 



Table 6.- 



— Average transpiration loss in 



winter of conifers and broad-leaved trees 





Tree type 





Jan. 17-24 



Mar. 21-24 





Percentage 

 of fresh 

 weight 



Percentage 



of dry 

 substance 



Percentage 

 of fresh 

 weight 



Percentage 



of dry 

 substance 



Conifers.- .__ ... ... _. . _ .. 



8.18 

 16.58 



19.72 

 37.74 



39.16 

 64.65 



93.90 



Broad-leaved--. - 



150. 18 











Ratio... . 



1:2.02 



1 :1.9 



1 : 1. 65 



1:1.6 







» This paper also has an added historical value, since the author cites some of the earliest experiments in 

 the field of transpiration, namely, those of Woodward in 1691 and of Hales in 1727. 



