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 mesophyll 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. secunda (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 hyphe in its outer cells. 
