1897] NORMAL AND DISEASED ORGANS OF ABIES BALSAMEA 341 
convex side of recurving branches, seldom contains any resin 
canals. 
Pith.—The diseased pith differs essentially from the normal 
in that its cells become thickened sooner, also forming larger 
groups of sclerenchyma cells. The cells of the pith area below the 
pith septum, which remain thin walled in the normal branches, 
become thickened in the diseased branches. Small areas of 
sclerenchyma cells are sometimes formed, which are never present 
in the normal. The internodal pith shows a greater develop- 
ment of mechanical tissue than in the normal branches. The 
diseased branches, which are correspondingly larger than the 
normal, also have a greater development of pith. 
SUMMARY OF THE MOST IMPORTANT CONCLUSIONS. 
Normal organs. 
I, Stomata are found in greater numbers toward the tips 
and on the lower surfaces of the leaves of the lateral shoots. 
The leaves of the terminal shoots have their stomata distrib- 
uted about equally on all sides. 
2. Hypodermal strengthening cells are always present in the 
leaves. They are seldom found in cross sections made above the 
middle of the leaves of the lateral branches. Below the middle 
they are usually found isolated on the upper leaf surface and in 
continuous layers on the lower surface. The shorter, rigid, and 
terete leaves of the terminal shoots have a greater development 
of hypoderm. 
= _ 3. The number of hypodermal strengthening cells decreases 
from the base toward the tip of the leaf; but with the decrease 
in the number of hypodermal cells there occurs a corresponding 
< increase i in the number of stomata. 
4. The transfusion tissue is not as well developed in the 
i leaves of the lateral branches as in the leaves of the terminal 
Shoots. In the former there are two small areas, each one lying 
_ dorsal to the outer half of the two phloem areas. In the leaves 
the terminal shoots the two transfusion tissue areas have 
