148 
a palisade-like transition-zone, a spongy parenchyma with large 
lacune, and lastly, just above the epidermis of the lower sur- 
face, a zone of from one to a few layers of elongated un- 
branched parenchymatous cells. The cells of the spongy paren- 
chyma are much branched — but their length is greatest in 
the direction of the longitudinal axis of the leaf — and they 
are exceedingly thick-walled. The intercellular spaces in the 
… spongy parenchyma take up considerable room. As gradually 
their number and size diminish towards the palisade-tissue, 
the walls become less thick, until in the palisade-tissue the 
cells are not characterized by any special thickness of wall 
although always proportionably thick when compared with those 
of the deciduous leaves. The elongated, unbranched cells 
above the epidermis of the lower surface are somewhat less 
thick-walled than those of the spongy parenchyma, neither have 
they among them the large intercellular spaces which occur 
in the spongy parenchyma, and they doubtless form a kind of 
protective tissue for the spongy parenchyma. The cells of the 
spongy parenchyma have well-marked pores. None of the 
Ericaceae I have investigated, not even forms with highly 
developed intercellular spaces such as Ledum and Arctostaphylos 
Uva-ursi, have such thickened walls in the cells of their 
spongy parenchyma as has Diapensia lapponica. 
Stereom is not developed around the vascular bundles. 
In the palisade-cells of specimens from Hekla Havn (East 
Greenland, Nov. 1891, N. Harrz) I have observed the Kraus 
winter-condition of the plasma. I also found in the leaves of 
these specimens, and especially in their palisade-cells, an 
abundance of tannin; on the other hand specimens from Godt- 
haab in the month of June did not give particularly good reac- 
tion for tannin. Oily substances, so far as they could distinctly 
be demonstrated to occur besides tannin (Sudan Ill, Osmic 
Acid [brown colour|), appear to be present in somewhat varying 
quantities at the different seasons of the year. Some summer- 
