— 148 — 



ing with the fact that the side nerves do not go from the upper 

 to the lower epidermis; at any rate the whole leaf always reacts 

 in the same manner. In Betula and Vaccinium uliginosum the 

 greater side nerves divide the mesophyl of the leaves into separate 

 parts and the infiltration appears very often in spots; it must then 

 be estimated how great a part of the leaf is infiltrated. It should 

 be added that for instance in Betula the whole leaf can react in the 

 same manner when either all or at least the greater part of the 

 stomata are open or closed to the same degree. 



The width of the stomata in Empetrum can not be estimated 

 in this manner; they are disregarded in this paper. 



3. Experiments. 



With the method described above two series of experiments 

 were carried out in the summers 1914 and 1915, in the following 

 manner: The rate of transpiration was estimated for each of the 

 4 plants at the same or about the same time. The experiments were 

 carried out between 11 a - m - and 4 p - m - and therefore hold good only 

 for this part of the day. There is reason to believe that the results 

 of the experiments would be the same also for the rest of the day; 

 during the night the transpiration will be less if the stomata are 

 closed. That was found to be the case in Vaccinium Vitis idaea. 



Care was taken that the branches used in the experiments 

 were grown in as favourable light conditions as possible. Using 

 shadow plants the values would be quite different, since the stomata 

 then would always be more or less closed. 



In the two summers the rainfall was in H i 1 1 e r ø d, 8 km from 

 Maglemose, the following: (in mm) 





March 



April 



May 



June 



July 



August 



Septb. 



Octb] 



1914 



80 



85 



39 



10 



95 



64 



53 



48 



1915 



43 



24 



77 



22 



111 



78 



60 



13 



Mean 



47 



37 



39 



49 



78 



82 



59 



78 



From the table it may be seen that in both years the month 

 of June was especially dry. Certainly the other summer months 

 were normal as to rainfall; but the dry early summer offered on 

 the whole rather bad conditions for the growth of the plants. 



The results of the experiments are given in Table 1 and 2. For 

 each experiment is calculated 1. the rate of transpiration pr. hour 



