WATER UTILIZATION BY TREES 



37 



temperature during this period ranged from —5.9° to 10.5° C, with 

 an average of 1.9°. The relative humidity was 39 to 74 percent. 



Even deciduous trees, however, lose water in winter. Hartig (89), 

 who was one of the earliest investigators in this field, placed tips of 

 twigs of various trees in closed test tubes. After about 24 hours 

 the test tubes were replaced with dry ones; the weight of the original 

 tubes showed the increase brought about by the moisture condensed 

 on the inside. On the basis of these rather primitive experiments, 

 he ranged plants according to the rate of water loss of their twigs 

 in the following" order: Alnus, Quercus, Robinia, Fagus, Juglans, 

 Betula, Tilia, Acer, Fraxinus, Pyrus, Aesculus, Ulmus, Salix. 



Burger (2k) in interpreting the work of Von Hohnel reported that 

 hardwoods lost only 0.5 to 2.5 percent of their annual water loss in 

 the winter, while conifers lost 8.5 to 12 percent of their annual tran- 

 spiration at this season. Larch (deciduous) in this respect is similar 

 to the hardwoods with a winter transpiration of 1.4 percent, while in 

 beech and spruce the corresponding figures are 1.5 and 12 percent, 

 respectively. Since these plants were in a closed though unheated 

 room, it is to be supposed that these figures are somewhat below 

 those under natural conditions. 



Wiesner and Pacher (241) found that transpiration in 2- or 3-year- 

 old twigs of Aesculus and Quercus continued at a noticeable rate 

 even at —3.5° to — 13° C, as indicated in table 14. They also studied 

 the transpiration of Aesculus twigs 1 to 30 years old, removing the 

 buds and sealing the cut places with wax. They found, among other 

 results, that the amount of water given off varied inversely with the 

 age, since the older twigs seemed to be better adapted for conserving 

 moisture. 



The following is a sample of their results: 



Age of twigs (years) and loss of water in 10 days at 15° to 

 17° C: . 



Percent 



1 11. 53 



2 10. 80 



3_ 



4_ 



5_; 



10. 

 15. 

 30. 



9. 46 

 6. 11 

 5.00 

 4.39 

 3. 47 

 1. 83 



Similar results were obtained by Ivanov (114) with 1- and 2-year- 

 old shoots of Aesculus glabra and Juglans cinerea L. The relative 

 rates of transpiration of the 1- and 2-year-old shoots in Aesculus 

 were as 4.59 is to 2.46 and in Juglans as 6.53 is to 4.25. 



Table 14. — Water loss at temperatures below 0° C. of twigs of Aesculus and Quercus 



in 24 hours 



Species and age 



Average 

 tempera- 

 ture 



Water loss 

 in 24 hours 



on basis 

 of original 



weight 



Aesculus, 2 years _. . 



°C. 



j -7.00 

 1 -9. 25 

 f -7. 00 

 \ -9. 25 



Percent 

 0.32 



Quercus, 3 years . _ .. _ ... _ .... 



. 20 

 .23 





.19 



