49 
same ring there is a gradual merging and not a sharp line of demarca- 
tion, as in the Yellow Pine (Pinus palu.st /is) or in the Tamarack (Larir 
Americana), The thick-walled cells in this wood are of a different char- 
acter from those of the two woods just mentioned; the cells are not as 
strong, the lumen being proportionately larger. The thin-walled tra- 
cheids, though not so large as those of the Yellow Pine, are generally 
quadrangular, and have the same proportionately large lumen, and the 
corners of the cells not being thickened they arc crushed more easily. 
Like the thin walled ones of the Yellow Pine, both classes of tracheids 
are u brash," and in breaking snap off quite short. So far as I have 
observed, the so-called "Yellow Hemlock" has a greater proportion of 
thick-walled tracheids in each layer than the " White Hemlock." 
The lines running down the page represent the medullary rays, and 
occur only in lines of cells of single width. The absence of resin-canals 
in this wood is in marked contrast to the Yellow Pine or Tamarack. 
In the White Cedar the dark and apparently solid cells shown in 
the transverse section are those of the longitudinally- arranged special 
resin-cells ; but none of these have as yet been found in the Hemlock, 
the resinous matter in this wood being much less abundant than in the 
other Conifers considered. In the transverse section what appears as 
small cells are those cut off near their tapering ends, and the swelling 
of the walls on the side in a plane parallel to that of the medullary 
rays is due to the cross-section of the lenticular markings; in the 
radial section these will be seen to be smaller and rounder than those 
of Yellow Pine or Tamarack, but larger than those of the Wliite Cedar. 
For a long time it has been the opinion that in the mature cell there is 
a free opening in the lenticular markings, the middle lamella breaking 
away. This is not found to be the case when examined with the high- 
est grade of objectives. In the large cells the lamella becomes crowded 
to the opening of the dome on the side where the sap is making its exit, 
and must be looked for with great care, while in some of the thick- 
walled cells it retains its central position and is readily seen. In the 
radial section the structure of the longitudinally-arranged cells is 
clearly shown, the harder, dense portion of the ring being seen on the 
left of the page. The lines running across the page represent the med- 
ullary rays. Above the upper row are seen the ends of the tracheids 
slightly rising as they approach the outer portion of the ring. 
In the tangential section the ends of the medullary rays are seen to 
be in single rows, the cells being superimposed one above the other. 
In a few instances only a single cell occurs, while in others there are 
two, three, and as many as twenty. These cells, as seen in the radial 
section, are short and easily parted, not binding the wood together 
firmly, as in the White Oak. The lenticular openings are abundant on 
the cell-walls parallel to the medullary plates. 
Durability. — The Hemlock is not a durable wood in contact with the 
ground, aud ties decay in about four years. The structure of the wood 
21753— Bull. So. 1 4 
