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Carsten Olsen. 



over the level of the other epidermal cells, more pronounced 

 on Arctic than Danish leaves. As to the number of stomata 

 on a given area, they are perhaps more numerous in the 

 Arctic specimens than in Danish. The table below gives 

 the number of stomata pr. Sq. m. m. of a number of Da- 

 nish and arctic leaves: 



Among other differences between leaves from the 

 Arctic and those from temperate localities, the following 

 is particularly pronounced and has shown itself to be 

 very constant: The Arctic leaf is thicker than the Danish 

 (fig. 4). This substantial difference is chiefly due to the strongly 

 developed spongy tissue of the Arctic leaf, while the length 

 of the cells of the palisade tissue is rather smaller than in 

 Danish leaves. Besides this, the Danish leaves have a more 

 loosely built mesophyll with the palisade cells only loosely 

 connected, diverging below, and the spongy tissue has large 

 intercellulars and more slender cells than is the case with 

 arctic leaves (fig. 4, C — D). The relation between the size 

 of the spongy tissue and that of the palisade tissue of 

 Arctic and Danish leaves is plainly given by the following 

 measurements of leaves from eight different Danish locali- 

 ties and a similar number from the Arctic. 



