95 
a protection against excessive transpiration (Fig. 10,1; Fig. 9, 1 
2,4). By the disorganization of these cells the large intercellular 
spaces are formed. Below the vascular bundle, which contains but 
very little stereom, a tissue occurs consisting of transparent cells 
(Fig. 10,2) which have far greater power of offering resistance 
to external factors than those in the spongy parenchyma and 
which resemble those 
HI ae 
te | 
that oceur in Andro- 
meda, but are not 
so compact and 
Re 2 i a 
US. 
ve 
ir 4 
. 4. / 
»-& sd 
h | 
sø 
pi" + 
have not the inter- 
== 
spersed thick-walled 
cells, occurring either 
singly orin trabecule. 
The leaf varies great- 
ly in thickness and 
breadth, sometimes i 
it is thick and narrow yy a7 | ; 3 ie Be 3 
(palustre), sometimes 8: i 
thin and broad (groen- 
landicum), but be- 
sides this there exist Fig. 12. Ledum palustre. 
hardly any differences Stem in transverse section; the limits of two annual 
of importance. rings are discernable; x 180. (Greenland). (Phot.) 
The stem. The primary cortex consists of a zone of 
small cells which occur just within the epidermis, which is 
hairy like the leaf and fairly thick-walled; internal to these are 
transparent, thin-walled cells mixed with a few with thicker 
walls, and trabecule of such thick-walled cells; while most 
internal are one to several rows of cells of the same form as 
the outermost ones. The pith, consists partly of transparent, 
thin-walled cells and partly of thick-walled cells, the latter 
occurring as trabecule between the former. 
The secondary cortex, which according to SEGERSTEDT is 
