135 



is the age-relationship, from a purely Arctic (Alpine) point of 

 view, which exists between the four above-mentioned species, 

 but 1 am inclined to believe that the species of Cassiope are 

 the oldest in that respect. 



The leaves of the deciduous forms scarcely suggest an 

 Arctic climate. They are all built more compactly than are the 

 leaves in the forms especially mentioned by Borgesen (1895); 

 but then il must be remembered that they occur also in moor- 

 land soil or at any rate in sour, peaty soil. Of these forms 

 only Vacc. uliginosum is common in the Arctic regions. Ana- 

 tomically it hardly differs from the southern forms. Judging 

 especially from the fact of Arctostaphylos alpina having larger 

 intercellular spaces it is doubtless less xerophytic than is 

 Vacc. uliginosum. Vacc. Myrtillus is scarcely sufficiently old- 

 established in the Arctic regions to be referred to the Arctic 

 Flora. 



Among the cases in which I have investigated the leaves 

 of southern specimens, only rarely have I been able to prove 

 that a lessening of the palisade-tissue accompanies further 

 advance southwards into the lowlands. But then it must be 

 remembered that the material has not in any way been com- 

 plete. In regard to the slight difference observed in the xero- 

 phytic structure of the North -European and of the Arctic 

 individuals of the same species, this may possibly — only 

 possibly — be due to the fact that winter-time, the most 

 dangerous time of the year, the time when evergreen leaves 

 need the greatest protection, does not in many points differ 

 greatly in the localities in question. 



All the species described in the present paper have tannin 

 in their leaves; most likely it is a family characteristic whicli 

 is useful to them in the Arctic regions. In some Danish and a 

 few Arctic specimens I have seen the plasma and the chloro- 

 phyll-contents of the evergreen leaves in the winter condition 



