91 
The leaf is strongly protected especially by its peltate hairs. 
The stem. The primary cortex consists of homogeneous, 
rounded cells, with larger or smaller intercellular spaces, and 
a thick epidermis. The secondary cortex consists of ordinary 
cork-cells. 
There is no 
re 
great difference 
between the 
327 
aie [1 
Par ER 
spring and sum- 
aie 
a 
eves 
= 
mer wood, and 
the limits between 
Aa 
the different an- 
ES x 
nual rings are 
not very distinct. 
Besides the ac- 
tual limits of the 
annular rings, 
which may be 
verified by cal- 
eulating the age 
of the portion of 
i Fig. 8. Rhododendron lapponicum. 
the branch in 
Stem in transverse section (Greenland). x 180. (Phot.) 
question from the 
number of its shoots, some confused boundary lines may often 
be discerned within the cortical zone of growth (O. G. Petersen, 
p. 78; Ampronn, 1890, p. 71). 
I have not examined the roots. 
Ledum palustre L. 
with f. decumbens Ait. and f. groenlandica (Oed.). (Figs. 9—12.) 
This species, whose occurrence in the Arctic regions is as 
, like the 
latter, specially characterized by the fact of its leaves being 
excellently protected. 
frequent as is that of Rhododendron lapponicum, is 
