110 College of Forestry 
merely a repository for the erystal and in so doing the walls 
usually become greatly distended. The wood prosenchyma 
elements compose the greater part of the dense outer portion 
of the annual growth ring and are relatively thick-walled. 
They have comparatively wide lumina and walls furnished 
with numerous small but distinct bordered pits, the orifice 
of which is slit-hke and usually oblique (Fig. 6). These 
elements have a constant structure and in shape and size 
resemble wood fibers more than tracheids. 
Microchemical Reactions of Normal Wood.— Cross sec- 
tions of normal wood, when treated with chlorzinc-iodine, 
exhibit comparatively ttle of the characteristic violaceous 
coloration indicative of cellulose. The middle lamellee of all 
the cells, the vessel walls, medullary ray cells, and the thin- 
walled wood parenchyma cells all color yellowish-brown. 
The wood prosenchyma elements exhibit a slight violaceous 
coloration which is strongest in the tertiary layer bordering 
on the cell lumen and fades off gradually tow: ard the middle 
lamella of each cell. This violaceous coloration is most promi- 
nent in the springwood elements and diminishes in intensity 
toward the outer face of the growth ring at which point it 
is scarcely distinguishable. In sections treated with phloro- 
glucin-HCl the thick vessel walls and the middle lamellee 
of all of the cells color most strongly, these becoming dark 
rose-colored or wine-colored. The remaining layers of the 
medullary ray and wood parenchyma cells are found to be 
tinted less strongly but still much more so than the remain- 
ing layers of the wood prosenchyma elements which appear 
almost violet. After treatment with aniline-sulphate-H.SO, 
the vessel walls and the middle lamelle of all the cells exhibit 
a brilliant golden yellow coloration. The remaining layers 
of the medullary ray and wood parenchyma cells likewise 
become strongly colored, but assume more of a brownish- 
yellow instead of the golden-yellow color. The remaining 
layers of the wood prosenchyma elements stand out much less 
strongly than the middle lamelle and appear to be of a pale 
lemon color. 
