122 College of Forestry: 
Tur Decay or Hemtiocx Woop. 
Structure of the Normal Wood.—The wood of the hem- 
lock [T’suga canadensis (Linn.) Carr.] varies from lght to 
medium weight, is soft, weak, stiff but brittle, coarse, and 
not durable in contact with the soil. The sapwood and heart- 
wood are not well defined. The heartwood is but little darker 
than the sapwood; its color may be described as light brown 
with a slight reddish hue. The medullary rays are very fine, 
numerous, and inconspicuous to the unaided eye. 
Microscopically the wood of the hemlock is of the non- 
porous type. Vessels are absent and the wood is composed 
of elements fairly uniform in structure. The contrast 
between the early and late wood is very decided, the transi- 
tion frequently being abrupt. The growth rings are defined 
by the greater density of the late wood. Resin ducts normally 
are lacking. The wood consists of (a) uniseriate pith-rays; 
(b) tracheids with bordered pits, and (c) terminal wood 
parenchyma cells. The rays are numerous, distant 2-10 
rows of tracheids, and vary from low to high. They are 
composed of two elements: (1) ray parenchyma cells with 
simple pits and (2) ray tracheids with bordered pits, the 
latter elements often interspersed, but mostly of marginal 
occurrence when viewed radially. According to Penhallow 
(1907, p. 267) the ray cells are somewhat contracted at the 
ends and average 3-5 spring tracheids in length. The upper 
and lower walls are very irregularly and often imperfectly, 
sometimes very sparingly , pitted. The terminal walls are 
not strongly pitted except in the summer wood. The lateral 
walls have small, oval pits, at first with a very narrow border 
which becomes more prominent toward the summer wood, 
the lenticular orifice becoming oblong; there are from 2-4, 
or in the summer wood from 1-2, pits per tracheid. 
The wood tracheids in the spring wood are large and very 
thin-walled, conspicuously squarish or often elongated radi- 
ally; furthermore, they are very uniform and in regular 
rows. In the summer wood they are more numerous, with 
thicker walls and smaller lumina, and in tangential section 
appear flattened, especially at the outer margin of the growth 
