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



The work of Montemartini (158) should be mentioned briefly. He 

 noted that in poplar the leaves at the ends of branches, i. e., the 

 younger ones, were the last to fall; while in the mulberry, the last 

 leaves to drop off were those at the base of the twigs, i. e., the oldest. 

 He explains this by the fact that transpiration in the poplar is chiefly 

 stomatal and the young leaves consequently control water losses 

 better. In the mulberry, on the other hand, the transpiration is 

 chiefly cuticular, and the oldest leaves are the better protected, i. e., 

 cutinized, and consequently are the last to fall. 



WINTER TRANSPIRATION 



In winter, conifers still transpire, although the transpiration rate 

 is very much reduced. Hartig (88) found that a Picea plant 3 feet 

 high lost one-fourth of a pound of water a day in a mild winter; but 

 since neither the leaf area nor the weight of the plant is given, this 

 paper is chiefly of historical value. 



Burgers tein (26) measured the transpiration of 1 -year-old twigs 

 of Taxus baccata L. with a special view to determining whether trans- 

 piration continued at low temperatures. He found, as shown in the 

 following tabulation, a gradual decrease in the transpiration rate as 

 the temperature decreased, but even at —11° C. there was a slight 

 water loss. 



Temperature (° C.) and loss of fresh weight per hour: 



Percent 



+ 17 1.5 



+ 12 . 9 



+ 4 . 6 



-2 .3 



-6 . 1 



-11 .02 



Ivanov (114) compared the transpiration in winter of 60 species 

 of trees and shrubs from the arboretum at Leningrad. One-year-old 

 twigs were cut and the cut surface closed with wax. The transpira- 

 tion rate was then determined by direct weighing and the loss in 

 weight calculated on the basis of the surface exposed. He used larch 

 as his standard and compared the others with it, employing the term 

 "relative transpiration." This is unfortunate, since (as has been 

 pointed out) "relative transpiration", as proposed by Livingston and 

 as used in the literature, has a very different meaning. Considering 

 Larix as 1, however, the following transpiration rates were found: 

 Abies sibirica Ledeb., 0.3; Pinus cembra L., 0.9; P. sylvestris, 0.6; 

 Picea obovata Ledeb., 0.8; P. excelsa, 1.5. The amount of daily loss 

 of water in winter in the moist climate of Leningrad was thus seen 

 to vary around 0.4 percent of the fresh weight of the needle-covered 

 twigs. The transpiration in summer was about 300 to 400 times as 

 great as that in winter. This figure does not compare unfavorably 

 with that obtained by Weaver and Mogensen (229), who found that 

 in winter in Nebraska the transpiration of conifers dropped from 

 one fifty-fifth to one two hundred and fifty-first of the autumn rate. 



Transpiration of conifers in winter in Japan was compared with 

 that of broadleaved evergreens by Kusano (181), who found that the 

 latter near Tokyo transpired an average of 16.58 g per square decimeter 

 of surface during the period January 17 to 24, while the conifers tran- 

 spired about half this amount per square decimeter (8.18 g). The 



