38 



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



Similarly young Taxus baccata twigs (deprived of leaves when cut) 

 lost water much more rapidly than older twigs, as shown by Wiesnei 

 and Pacher {241), who report the results shown in table 15. 



Table 15. — Water losses in first 6 days after cutting and removal of leaies from Taxus 

 oaccata twigs of different ages 



24-hour interval 



Water loss (on fresh-weight 

 basis) of— 



24-hour interval 



Water loss (on fresh-weight 

 basis) of— 



2-year-old 



twigs 



3-year-old 

 twigs 



4-year-old 

 twigs 



1 



2-year-old 3-year-old 



twigs twigs 



4-year-old 

 twigs 



First 



Percent 

 28.5 



15.1 

 3.0 



Percent 

 16.4 

 11.7 

 8.5 



Percent 

 8.5 

 7 2 

 «C"4 



Fourth 



Percent 

 1.2 

 .4 



.4 



Percent 

 6.1 

 2.8 

 1.2 



Percent 

 4.5 





Fifth 



3.7 



Third 



j Sixth . 



2.9 









Kny {125) placed sections of winter branches of broad-leaved trees 

 in a room at 15° C, noting the water losses. In Fraxinus excelsior, 

 Acer pseudoplatanus, and Utmus scabra Mill, the losses were consider- 

 ably greater between the nodes than at the nodes where the buds are 

 located, while in Carpinus betulus and Aesculus hippocastanum there 

 was little difference in this respect between the stem sections. Buds 

 of Syringa, Fraxinus, and Aesculus showed larger losses in weight when 

 the leaf scars were plugged up. There is no doubt, therefore, that 

 1-year-old twigs can lose considerable amounts of water through tran- 

 spiration during a dry whiter. 



A large part of the evaporation from the twigs is from the lenticels, 

 which various researchers have shown serve for gaseous exchange on 

 the young twigs in very much the same way that the stomata serve 

 on the leaves. Haberlandt (79) thought that the lenticels were closed 

 much of the time even in summer in many trees (e. g., Tilia and 

 Robinia). These results, however, were not supported by the work 

 of Klebahn {123), who concluded from the results of studies on over 

 70 different species that (1) lenticels are open both in summer and 

 winter and that (2) in many cases their permeability is nearly as 

 great in the winter as in the summer. 



It is also interesting to note in this connection that the lenticels are 

 much less permeable to air (and the contained moisture) when moist 

 than when dry. As pointed out by Zahlbruckner {24-7), differences 

 were especially noticeable in Ailanthus altissima Swingle, Alnus gluti- 

 nosa, Caragana frutescens DC, and Pauloicnia imperialis Sieb. and 

 Zucc. 



The relative proportion of the transpiration from the twigs through 

 the lenticels has been studied especially by Haberlandt and Klebahn. 

 The cut ends of the twigs were closed with wax or lacquer and drops 

 were placed over the lenticels. Similar twigs were prepared in which 

 the same number of drops of wax were placed between the lenticels, 

 and the relative water losses of the two twigs were then compared, 

 differences being considered as due to the lenticels. Klebahn found 

 that twigs of Moras alba in 3 days lost 46 percent of their original 

 weight when the lenticels were closed and SO percent when they were 

 open. This loss of water from deciduous trees in winter may be con- 

 siderable in the aggregate, and it is doubtful whether all foresters have 



