The Biology of Polyporus Pargamenus Fries 105 
vessels occur singly or in radial groups of from two to five, 
or rarely six. The vessel walls, at their points of contact 
with one another and where they border on ray or wood 
parenchyma, are provided with densely packed and rather 
large bordered pits, the borders often hexagonal owing to 
crowding. The interior walls of the vessels are provided 
with spiral thickenings. The wood parenchyma is developed 
to a limited extent, the walls remaining comparatively thin. 
It occurs sparingly on the radial sides: of the vessels and is 
also to be found seattered irregularly over the outer face 
of the summerwood. The individual cells of wood paren- 
chyma, as well as the ray parenchyma, responded to the 
iodine test for starch, since the wood was cut late in the 
autumn. Chambered parenchyma containing crystals occurs 
occasionally but was by no means common in the sapwood 
studied. The wood prosenchyma has simple pits and the 
elements are of the nature of typical wood fibers. These 
elements sometimes contain starch. The growth rings are 
defined mainly by a tangential flattening of the outermost 
cells and by the somewhat smaller size of the vessels in the 
late wood (Plate XXIII, Fig. 1). 
Microchemical Reactions of Normal Wood.— Cross see- 
tions of normal wood, when treated with cellulose reagents 
such as chlorzinc-iodine, exhibit comparatively little of the 
characteristic violet coloration indicative of cellulose. The 
middle lamelle of all the cells and the entire walls of 
the vessels and medullary rays all color yellowish-brown. 
Certain of the prosenchyma elements, particularly those on 
the outer face of the late wood, exhibit a slight violaceous 
coloration in the secondary and tertiary layers. The major- 
ity of the prosenchyma elements, however, exhibit little or no 
such coloration with chlorzinc-iodine. In sections of wood 
treated with phloroglucin-HCl the vessel walls and the 
middle lamellee are colored most strongly, becoming reddish- 
violet. The remaining layers of the medullary ray “cells like- 
wise become reddish-violet and appear to be stained almost 
as deeply as the vessel walls. The secondary and tertiary 
