280 Elg. Warming. 



the summer; it is advantageous that transpiration is not lessen- 

 ed by special structural features, so that the water-current can 

 flow rapidly through the leaves and the assimilation increase 

 in vigour and compensate for the briefness of the summer, 

 with its fogs and weak light. The transpiration cannot be 

 assumed to be specially strong during summer. It is also 

 easily compensated for by the water which is accessible to 

 the herbs from the fogs and from the water-contents of the 

 soil. 



The precipitation undoubtedly varies greatly in the 

 different regions. Lundager records from Danmarks Havn 

 in N.E.Greenland 28.4mm for the summer (April — Sept.) 

 and 117.2 mm for the winter. Only 1 / 10 falls as rain. The 

 inconsiderable amount of rainfall must undoubtedly be 

 compensated for by the water-contents of the soil and the fogs. 



Thorild Wulff has, in his paper of 1902, communi- 

 cated some results of transpiration-experiments with Arctic 

 plants made with the cobalt-test in the open in Spitzbergen, 

 detached leaves being placed between cobalt-paper. Wulff 

 particularly emphasizes the fact that the method is defec- 

 tive, but no other could be employed. The water from the 

 snow of the habitat situated on a high level "provided for 

 a homogeneous distribution of the moisture of the soil." 

 Unfortunately, he did not investigate the temperature of 

 the water and the soil, which of course plays an essential 

 part as regards the amount of the transpiration. Among the 

 ten species which were investigated, there was only one of 

 Caryophyllaceæ, viz. Cerastium alpinum, the leaves of which 

 were woolly with dense hairs. The transpiration was exceed- 

 ingly slight, which Wulff thinks was essentially due to the 

 hairy covering, '"as the anatomy of the leaf rather favours 

 the belief in an excessive transpiration than tells against it." 

 Among the plants used for the experiment, Cerastium alpi- 



