137 



the theory that the short period of growth hi the Arctic regions 

 is the cause of this slight ditîerentiatioii. But in spite of 

 this it does not follow that the short period of growth is of 

 no importance whatever in this connection ; it is undoubtedly 

 instrumental in lessening the difference between the different 

 elements of the wood; but as yet there hardly exists any accurate 

 data on this point. In some cases other circumstances, such 

 as slight need of stereom (in the case of prostrate stems), are 

 doubtless of importance. 



Lastly if, with reference to what I have indicated in the 

 introductory lines, I am to point out the species which are 

 most in conformity with the Arctic climate, then among the 

 evergreen species it must be ßhododendron lappouicuin^ and 

 to a certain extent Ledum and Cassiope tetragona (Cassiope 

 hypnoides also in a measure) and among the deciduous species 

 Vaccin iimi uliginosiim . 



It is only the structure of the leaves which is of importance 

 in this connection, the stem and the root not shewing any 

 special points of interest in this respect. Among the evergreen 

 species, the greatest progress has doubtless been made by 

 Rhododendron lapponicimi and Cassiope tetragona — both true 

 Arctic species which have most probably been long-established 

 in the region in question, — and only such evergreen species 

 as have, each in its own way, assumed the degree of protec- 

 tion attained by these two, will be able to continue to exist in 

 the Arctic climate. Among the deciduous species such decided 

 differences are not to be found as occur among the ever- 

 greens. 



