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Fig. 2. Adenophorus sarmentosus. 1—31, Selected serial cross-sections of the stele of the rhizome showing 
origin of leaf traces and root traces. 
of slightly thinner-walled, protoplast-containing 
cells often occur, usually directly opposite a 
departing leaf trace. The outer 2 or 3 cortical 
cell layers are composed of uniformly large 
parenchyma cells. The cells of the single-rowed 
epidermis are thin-walled. 
The xylem cylinder is from one to three cells 
thick. Its tracheids are of relatively uniform 
size. The protoxylem tracheids are only about 
V 2 the diameter of the average metaxylem ele- 
ments and are grouped in more or less distinc- 
tive areas on the outer margin of the xylem 
cylinder. The xylem, therefore, is apparently 
exarch. Within the cylinder of xylem, the cells 
of the one-layered or occasionally two-layered 
internal phloem are separated in most instances 
from the xylem by a layer of parenchyma cells 
similar in structure to the cells of the central 
pith. Another layer of parenchyma also occurs 
between the xylem and the outer phloem. The 
cells of the outer phloem are conspicuously 
smaller than those of the inner phloem and 
