AMERICAN JOURNAL OF BOTANY 
[Vol. 8 
in a wall of plane ashlar masonry. The walls of their cells are only moder- 
ately thickened, and their lumina are often filled with starch. The medul- 
lary rays are most noticeable in the lower part of the stem and in the roots. 
One small root had five primary medullary rays. 
The difference between fall and spring wood rests partly on the dis- 
similarity of the wood fiber cells and partly on that of the vessels. The 
first tracheals of spring are larger, thicker- walled, and stretched somewhat 
radially, while those toward the outer border of the annual ring are flattened 
to smaller, thicker-walled, and radial rings. The vessels in the spring wood 
are wider and more numerous, in the fall wood narrower and scarcer, as 
shown in Plate III, figure 3. The breadth of the annual rings varies. 
The inner wood is colored yellow or yellow-brown. A great deal of this 
coloring matter can be extracted with hot alcohol. This extract behaves 
similarly to the extract of the related species Rhus Cotinus L. (Cotinus cog- 
gygria Scop.) in the following treatment: an orange-yellow solution in water 
was made bright yellow by hydrochloric acid, yellow-red by ammonia, orange 
N. with alum and sodium carbonate solution, and brown N. by calcium 
chloride solution. Such a behavior by no means proves that the solutes 
from the wood of Rhus diver siloha are identical with those from R. vernicifera, 
although such may actually be the case. The coloring matter is naturally 
attached to the membrane of the wood cells, which appear golden yellow 
under the microscope and assume a brown color with caustic potash. Be- 
sides the yellow crystals, the wood cavities contain a reddish amorphous 
resinous substance which is likewise soluble in 95 percent alcohol. 
The primary cortex contains sclerosed parenchyma. 
The structure of the pericycle is characteristic. It contains many bast 
fibers, which, in transverse section, have the form of arcs whose convex 
sides are on the exterior and whose inner concave surfaces surround in each 
case a single, usually large resin duct (PI. Ill, fig. 5). 
The resin canals in the later-formed portions of the bark have a lumen 
and are arranged more or less regularly in concentric circles as heretofore 
described. The old resin canals appear to be obliterated through a kind of 
tylotic growth. On one transverse section through the bark of an old stem 
which has already thrown off the primary covering there are many resin 
canals differing in form, outline, and dimensions. The innermost are 
open and nearly circular, but usually more strictly oval in shape, stretched 
tangentially, and of larger circumference than the outer ones. The outer- 
most, particularly in old stem parts, are entirely or almost entirely obliter- 
erated through the luxuriant growth of intruding contiguous tissue. It is 
possible to observe at different heights of the same resin canal different 
states of development so that in one place it may still be open and in another 
closed. This occurrence of tyloses in the secretory ducts is similar to that 
described by Mobius (22) in Rhus vernicifera L., by Leblois in Brucea fer- 
ruginea, and by Conwentz in the intercellular canals of other plants. 
