SAMBUCUS PUBENS VAR. XANTHOCARPA 179 
The endodermis (En) is quite regular and clearly distinct from 
the cortical cells around it. The cortical parenchyma cells are 
round in outline of cross section and the hypodermis is very 
distinct.. 
A cross section of the hypocotyl (Fig. 6) shows the stele nearly 
filled with xylem (Xy). The secondary xylem pushes out the 
cambium (Ca) and this then constitutes four layers of cells. The 
phloem (Ph) encircles the xylem which completely fills the inner 
part of the stele, there by showing the absence of pith. The xylem 
is fully developed. The cross section was made from a point high 
up the length of the stem. 
COTYLEDON AND ITS PETIOLE. (Fig. 9). 
As a general rule the cotyledon is notched at its apex and 
has one closed collateral wood bundle with xylem (Xy) to the 
upper and phloem (Ph) to the lower side. Chlorenchyma is found 
‘in the intervening space between the stele and epidermis (Ep). 
A distinct hypodermis (Hy) is present just below the epidermis. 
The petiole of the cotyledon is in no way different from that 
of the leaf, which will be discussed later. 
The upper and lower epidermis (Fig. 7) of the cotyledon have 
about the same structure. The cells are very irregular in shape 
and the stomata contain chlorophyll grains and are more numerous 
upon the ventral face than upon the dorsal surface. Intercellular 
spaces (IS) are found interposed between the cells of the chloren- 
chyma (Fig. 8). 
EpicotyL (Fig. 10). 
The epicotyl in early growth soon has about twelve collateral 
woodbundles, two of which are shown in the illustration. ‘Three 
layers of cells constituting the cambium (Ca) and very little 
differentiated from the phloem (Ph) in size and shape, are inter- 
posed between the xylem (Xy) and phloem. Wood parenchyma 
cells are interspersed bettween the cells of xylem. The pith (Pi) 
consists of cells of regular outline. The parenchmya (Pa) is com- 
posed of cells of irregular size. A hypodermis (Hy) is found beneath 
the epidermis (Ep) which apparently consists of two layers, the 
outer layer of which is not very much thickened as is usually the 
case. 
PETIOLE OF THE LeaF. (Fig. 11). 
' The cross section of the petiole of the leaf is circular in out- 
