418 



Fr. J. Mathiesen. 



from the stele, compare Fig. 17, Z>, which is a diagrammatic 

 representation of a part Ике the one just described — the 

 section was taken between the uppermost scale-leaf and the 

 first pair of foliage-leaves), small groups of sieve-tissue 



A 



Fig. 18. Bartschia alpina. 



A and B, Transverse sections of foliage-leaves. С and D, Portions of 



the epidermis of the upper and of the lower surface respectively. (West 



Greenland.) [A and 5, about 1«%; С and D, about 220/^.) 



elements, however, are always found enclosed in the stereom 

 (well-illustrated in Hovelaque's Fig. 334, p. 405). 



Medullary rays do not occur. The epidermis of the rhi- 

 zome persists for a long time; cork is not developed (Holl- 

 stein); in the older rhizomes a successive dying-away of the 

 outer layers of the cortex takes place. 



The Leaf. The epidermal cells of both the upper and 

 the lower surface have undulating lateral walls, this being 

 somewhat more strongly the case with those of the lower 

 surface than with those of the upper (Fig. 18, С and D). 



