. 
The Biology of Polyporus Pargamenus Fries 117 
tered, thin-walled fibers. The former have occasional minute 
simple pits and are of the nature of typical wood fibers; 
the latter have numerous, more or less narrow, oblique bor- 
dered pits and resemble typical tracheids. The thick-walled 
wood prosenchyma elements are very fine, thread-like cells 
about 1.31 mm. long and 0.020 mm. wide. They occur in 
large compact groups alternating with the radial rows of 
more or less minute vessels of the late wood and are traversed 
radially by the uniseriate pith-rays and tangentially by irreg- 
ular, more or less broken rows of wood parenchyma cells. 
The thin-walled wood prosenchyma elements occur scattered 
among the vessels, both the large vessels in the early wood 
and the radial rows of small ones in the late wood. ( Plate’ 
XXV, Fig. 1.) The bordered pits in these prosenchyma ele- 
ments are present irrespective of whether the contiguous 
elements are vessels, thick or thin-walled prosenchyma, or 
wood parenchyma cells. Except for the differences in the 
pitting of their walls, the thin-walled wood prosenchyma ele- 
ments are essentially the same as the thick-walled ones. 
Tracheids are single fiber-like elements and are, therefore, 
easily distinguished from the vessels since the latter are 
formed by the fusion of cells placed end to end. In trans- 
verse sections, however, it is more difficult to separate them 
from the very small vessels. 
Microchemical Reactions of Normal Wood.— Cross sec- 
tions of normal wood, when treated with chlorzinc-iodine,* 
exhibit comparatively little of the violaceous coloration 
indicative of cellulose. The large groups of thick-walled 
wood prosenchyma elements are the only elements to exhibit 
any appreciable violaceous color. The middle lamellae of 
all the cells and the entire vessel walls are colored a golden 
brown. Both the secondary and tertiary lamelle of the 
tracheids, the wood parenchyma and the ray parenchyma 
cells are colored a lighter brown than the middle lamelle 
and exhibit little or no violaceous coloration. The ray 
parenchyma cells and the wood parenchyma fibers were very 
conspicuous after staining with chlorzinc-iodine, due to the 
