POLYGONATUM COMMUTATUM _ - 7 
is enclosed by an epidermis (dermatogen) (a) with a slightly 
thickened outer wall. 
THE COTYLEDON AND ITS PETIOLE (FIG. 10). 
These have two wedge-shaped closed collateral bundles 
with xylem (d) directed inward and phloem (c) outward. These 
bundles are produced by the splitting of the single flattened 
bundle of the hypocotyl as shown in the diagram (Fig. 12). They 
are very well developed since all the water entering the seed and 
the entire food supply which is derived from it must pass through 
them. The remaining portions of the cotyledon are made up of 
simple parenchymatous tissue (b) with a thin walled epidermis (a). 
THE EPICOTYL. 
The epicotyl of a germinating seedling is made up of embryonic 
parts which have no marked vascular structure. Later its makeup 
is much the same as that of the mature rhizome into which it 
develops. 
HISTOLOGY OF THE MATURE PLANT. 
THE ROOT (FIG. 21). 
The epiblema (a) of the ‘root is composed of rather thin- 
walled cells somewhat elongated lengthwise of the root. Beneath 
these is a peculiar layer of enlarged cortical cells (b) having a 
palisaded appearance as in the primary root. ‘The remainder of 
the cortex is made up of smaller cells (c), and in young roots is 
from eight to ten cell layers in thickness. Next in order are a well 
marked endodermis of thin walled cells (d), and a pericycle sur- 
rounding the central stele. The stele itself is of the radial type 
with from three to seven exarch xylem (hadrome) rays (g) and 
alternating phoelm (leptome) strands (f). Fig. 22 is a cross section 
of a heptarch or seven rayed bundle from a young root tip, showing 
the innermost layer of ordinary cortical cells (a), the endodermis 
(b), and the pericycle (c) before the cells have taken on their ordinary 
flattened appearance. Only the protoxylem (d) and protophloem 
(e) have been formed, the rest of the conducting tissue being as 
yet undeveloped. The large cells (f) embedded in the pith (g) 
form metaxylem a little later. 
THE RHIZOME (FIGS. 18 and 19). 
In the rhizome will be seen first the epidermis (Fig. 18,a, 
Fig. 19, a) of flattened brick-like cells with a thickened outer wall. 
‘Beneath these is the cortex (Fig. 18, b, Fig. 19, b) of roughly 
