82 



and fewer in number towards the upper surface of the leaf, 

 larger and more numerous towards the lower surface of the 

 leaf, where the rnesophyll may begin to resemble spongy paren- 

 chyma, but cannot actually be termed spongy parenchyma. 

 Especially in this part of the leaf the intercellular spaces 

 impress one as rather curious, as it appears that they are not 

 formed normally between 2 — 3 or more cell-walls, but by the 

 walls of two adjoining cells separating from each other (Fig. 1, 7), 

 That this can really be the case may be proved by comparing 

 the corresponding circumstances in Fir. secimda (Fig. 3, 2|. 

 Here we are undoubtedly dealing with a kind of secondary 

 intercellular-space-formation. All the cells of the leaf give the 

 reaction for tannin, but least is given by the central cells of the 

 mesophyll. In this point the Greenland specimens of this species 

 differ from the Danish individuals of Pir. rotundifolia which is 

 otherwise very closely related to Pir. grandiflora; the Danish 

 Pir. rotundifolia has cells in the centre of the mesophyll which 

 are entirely devoid of tannin, forming a distinctly transparent, 

 central area. There is no stereom developed around the veins 

 of the leaves. Hydathodes occur over the termination of the 

 vascular bundles (Fig. 1,3). 



The stem. From a biological point of view the structure 

 of the stem presents no feature of any great interest. In the 

 young stem a layer of cortical cells occurs under the epidermis — 

 thick-walled like the latter, and devoid of starch. When the 

 primary epidermis falls off, a kind of cork is formed consisting 

 of angular cortical cells. There is no regular periphery, but 

 the older formations persist for a long time. The other parts 

 of the structure of the stem present no point of interest beyond 

 the fact that the inner cortex consists of large parenchymatous 

 cells, abundantly filled with starch, and that annual rings may 

 occur in the central cylinder. 



The root has endotrophic hyphae in its outer cells. 



