- 150 — 



1915 



7« 



13 /e 



2 % 



2 7v 



25 / 7 



15/ 



Is 



29/ 

 /8 



12/ 

 /9 



Mean 



Empetrum 



7 



6 



13 





19 



13 





6 



11 



Vacc. Vit. idaea 



7 



5 



14 



14 



16 



14 



18 



11 



12 



Vacc. uligin. . . . 



7 



7 



16 



14 



18 



14 



12 



15 



13 



Betula 



8 



5 



20 



18 



21 



14 



15 



10 



.14 



Considering the values for the relative transpiration the mean 

 for the different plants is the following: 



Empetrum 11 



Vacc. Vit. idaea . . 13 



Vacc. uligin 15 



Betula 14 



From these figures we learn the following : 1. The difference 

 between the rates of the relative transpiration for the 4 species is 

 rather small. In Empetrum the transpiration is rather less than in 

 the other 3. But in Vacc. Vit. idaea with the coriaceous leaves 

 the rate of transpiration is about the same as in plants with thinner 

 leaves Betula and Vaccinium uliginosum. This result may seem to 

 be curious. Yet it should be mentioned that Bergen (1904) has 

 found that also in other plants the effect of xeromorphy on trans- 

 piration may be rather small: 



Transpiration pr. 100 cm 2 leaf area, mg 



Olea 302 Bhamnus 658 



Pistacia 231 Ulmus campestris .... 342 



Quercus Ilex 238 Pisum sativum 353 



2. Further it should be noticed that the rate of the relative 

 transpiration on the whole is rather small. For comparison some 

 estimations carried out by D e 1 f (1912) may be mentioned here: 



Relative tranpiration pr. hour pr. sq. dem. 



Water 100 



Salsola Kali 64.1 



Mesembryanthemum 66.9, 47.6 



Atriplex 61.7 



Salicornia 32 



Sedum sp 36 



Saponaria 27.6, 7.4 



Vicia Faha 26.0 



Aster Tripolium 22.4 



