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 

 great difference 

 between the 

 spring and sum- 

 mer wood, and 

 the limits between 

 the different an- 

 nual rings are 

 not very distinct. 

 Besides the ac- 

 tual limits of the 

 annular rings, 

 which may be 

 verified by cal- 

 culating the age 

 of the portion of 

 the branch in 

 question from the 



number of its shoots, some confused boundary lines may often 

 be discerned within the cortical zone of growth (0. G. Petersen, 

 p. 78; Ambronn, 1890, p. 71). 



I have not examined the roots. 



Fig. 8. RJiododendrov Jcqjponicum. 

 stem in transverse section (Greenland), x 180. (Phot.) 



Ledum palustre L. 



with tdecumbens Ait. and f. groenlandica (Oed.). (Figs. 9 — 12.) 

 This species, whose occurrence in the Arctic regions is as 

 frequent as is that of Rhododendron lapponicum, is, like the 

 latter, specially characterized by the fact of its leaves being 

 excellently protected. 



