200 Fr. J. Mathiesen. 



The total number of stomates per leaf is, however, on an 

 average far greater on specimens from Öland, than on those 

 from Arctic America and Siberia. 



The apex of the leaf and of each of the 2 — 4 teeth 

 in its margin, are provided on the lower surface with a group 

 of hydathodes, from which the distal portion of the veins 

 extends fan-shaped as a well-developed epitheme. 



A transverse section (Fig. 17, C) discloses from 2 — 4 layers 

 (the thickness of the leaf is somewhat variable) of short 

 and broad palisade cells, which like the rest of the mesophyll 

 are rich in chlorophyll granules. The undermost layer of 

 the mesophyll consists of rather strongly branched cells. 

 Frequently the epidermis of the lower surface is found 

 loosened from the mesophyll. The vascular bundles are 

 sometimes accompanied by cells with collenchymatous thicken- 

 ing (fig. 17, C, the vascular bundle to the left). In the epi- 

 dermis of both lower and upper surfaces, though most fre- 

 quently in the latter, there are cells filled with a brown 

 substance. In all the leaves examined by me, but only in 

 the upper surface, this contains some peculiar spheroidal and 

 deeply brown-coloured bodies (fig. 17, G), which were ex- 

 ceedingly resistant towards solvents; they may perhaps be 

 only a precipitate caused by evaporation, or by preserva- 

 tion in alcohol. 



With regard to the floral parts of A. septentrionalis, the 

 calyx presents a peculiar anatomical structure, so that it 

 deserves further attention. 



A transverse section (fig. 18, A) of one of the 5 pro- 

 jecting ridges of the calyx (see p. 196) shows a layer of thin- 

 walled cells within the epidermis of the outer surface of the 

 calyx; these cells are in close contact with each other, and 

 also with the epidermis without any intercellular spaces. This 

 layer (probably an aqueous tissue) is seen in fig. 18, B, 

 in surface-view; its elements appear very elongated, with 



