78 



MISC. PUBLICATION 257, U. S. DEPT. OF AGRICULTURE 



5 to 7 years old which were regularly watered and weighed during 

 three entire growing seasons. At least two plants of each species 

 were used, and his calculations were recorded in kilograms of water 

 per 100 g of air-dry weight of leaves per growing season. His average 

 results are given in table 28, column 1. 



Table 28. — Average water loss per growing season and per day of polled trees of 

 various species, per 100 grams of air-dry weight of leaves 



Species 



Water loss 



per growing 



season > 



Water loss 

 per day } 



Species 



Water loss 



per growing 



season > 



Water loss 

 per day 2 



Fraxinus _ ... . 



Kilograms 

 85.6 

 81.4 

 74.9 

 73.1 

 66.2 

 58.6 

 53.2 



Grams 

 400 

 380 



350 

 340 

 308 

 274 

 255 



Acer platanoides . 



Kilograms 

 53.1 

 45.3 

 13. 5 

 9.4 

 7.0 

 6.7 



Grams 

 248 



Betula.. . 





212 



Fagus .. . 





63 



Carpinus . . 





44 



litmus 





34 



Acer pseudoplatanus 





31 



Quercus pedunculata 







i These figures are taken from Horton's (103) comprehensive analyses of the work of Von Hohnel. 

 » As calculated by Ebermayer (55). 



There are several objections to the work of Von Hohnel. In the 

 first place, the vessels contained only about 8 to 12 pounds of soil — a 

 very small amount for trees of that size. Hermetically sealing the 

 pots must also have resulted in unfavorable conditions for the roots, 

 which probably explains the high mortality encountered. Also it 

 has been suggested by Morosov {159, p. 113) that the internal tem- 

 perature of the zinc pots was probably too high. As individual 

 experiments, however, without reference to older trees or larger areas, 

 Von Hohnel's figures agree fairly closely with those of other workers, 

 and Morosov thinks they are still as good as any available. 



In the more recent European work Vyssotsky, as given by Morosov 

 (159, p. 112), records the following water losses in 1 hour, expressed in 

 percentages of the original weight: 



Percent 



Ulmus campeslris 19. 



Acer platanoides 10. 5 



Quercus 9. 6 



Fraxinus 9. 4 



Acer campestre 8. 



Pinus sylvestris 2. 1 



Pinus laricio . 7 



The high rate for elm is considered to be due to its thin cuticle. 



Huber (105) compared the relative transpiration of cut branches; 

 his results are shown in table 29. It must be remembered that the 

 relative transpiration shows the control exercised by the plant over 

 water losses as compared with evaporation from a free (atmometer) 

 surface. 



Table 29. — Relative transpiration of cut branches of various tree species 



Species 



Transpira- 



ation in 1 



hour per 



gram of 



fresh weight 

 of leaves 



Relative 

 transpira- 

 tion 



Species 



Transpira- 

 ation in 1 

 hour per 

 gram of 

 fresh weight 

 of leaves 



Relative 

 transpira- 

 tion 



Betula . ... 



Milligrams 

 190 

 202 

 149 

 87.4 



0.59 

 .34 

 .33 

 .16 



Fagus: 



Milligrams 

 51.5 

 41.9 

 23.5 

 10.7 



0. 11 







.07 







.15 







.06 









