180 THE AMERICAN MIDLAND NATURALIST 
line and has three closed collateral ‘woodbundles. The xylem 
(Xy) is inward and the phloem (Ph) outward. Cortical parenchyma 
occupies the intervening space between the stele and the epi- 
dermis and a distinctive hypodermis (Hy) does not exist. The 
epidermis (Ep) is composed of cells longer than broad with a 
thickened cuticle. 
THe Lear. (Fig. 12). 
The epidermis of the leaf, dorsal as well as ventral is com- 
posed of cells not unlike those of the cotyledon and in general 
has the same appearance. The cells are flattened and diminish 
in chlorophyll content towards the outside. There are large 
intercellular spaces between the chlorenchyma cells. The epi- 
dermis (Ep) shows a greater thickening in its walls than in those 
of the adjoining cells. 
CONCLUSION. 
1. Pith is absent in the primary root and hypocotyl of the 
young seedling,but is present in the upper part of the hypocotyl 
and epicotyl. 
2. The plant at first produces simple leaves but by a series 
of transitional stages compound leaves are formed, the apical 
leaf being the largest. 
3. As the lower part of the hypocotyl matures the entire 
center of the stele is filled with xylem and no pith is to be found. 
EXPLANATION OF THE FIGURES. 
Fig. 1. Seedling showing the emergence of root, hypocotyl, and 
cotyledons from the seed. : 
Fig. 2. A more advanced stage of the seedling showing the coty- 
ledons, hypocotyl, root and two young leaves. 
Fig. 3. Cross section of the primary root. (Ep) Epidermis, (Hy) 
Hypocotyl, (CP) Fundamental parenchyma, (Hn) Endodermis, (Pi) ere: 
(Xy) Xylem (Hadrome), (Ph) Phloem (Leptome). 
Fig. 4. Cross section of a very young hypocotyl. (Ep) Epidermis, 
(CP) Cortical parenchyma, (En) Endodermis, (Xy) Xylem, (Pe) Peri- 
cycle, (Ph) Phloem. 
Fig. 5. Cross section of hypocotyl. More advanced stage than the 
preceding. (Ep) Epidermis, (Hy) Hypodermis, (Pa) Extrastelar Paren- 
chyma, (En) Endodermis, (Ph) Phloem, (Ca) Cambian, (Xy) Xylem. 
Fig. 6. Cross section of hypocotyl, showing still further development. 
Wood bundle alone is illustrated. (Pa) Parenchyma, (Ca) Cambium, 
(Xy) Xylem, (Ph) Phloem. 
Fig. 7. Surface view of ventral epidermis of cotyledon. Illustration 
