478 DR. P. GROOM AND MR. W. RUSHTON ON THE STRUCTURE 
on a ray-tracheid the transverse terminal wall has one or more bordered 
pits. With this exception and the sporadice occurrence of pits on the tan- 
gential and terminal walls, the bordered pits are confined to the radial walls, 
where in the spring-wood they are uniseriate or biseriate or both in the same 
tracheid (fig. 26). In each primary pit-area there may be one bordered pit 
or two collateral ones. Here the bordered pits are circular or oval with the 
longer axis transverse and the orifices circular, or widely fusiform and with 
the longer axis directed transversely, obliquely or nearly vertically. In the 
summer-wood the seantier and smaller pits are circular with a narrow 
fusiform, nearly erect orifice (fig. 21). 
The peculiar structure shown in figure 22 and superficially resembling a 
deformed bordered pit is a transverse section of a radial bar (Nanio's bar) 
which streatehes across the lumen of the tracheid and perhaps increases in 
height near its attachment to the tangential wall. 
Resin-Ducts. 
The resin-ducts may be solitary or paired, and in the latter case separated 
by only a few layers of flattened thin-walled parenchyma. The ducts have 
an unusually wide cavity (the width of which attained *2 mm., while the 
radial width of the epithelial cells was 13 ш). The cells composing the one- 
layered epithelium in longitudinal section are short, broad, often elongated 
transversely and hexagonal in form. 
This layer may be wholly or partially enveloped in a sheath of flattened’ 
parenchyma. 
Surrounding these cells is thin-walled parenchyma, whose ceils are briek- 
shaped, and elongated longitudinally. Such cells are often particularly 
developed on the side towards the nearest medullary ray, with whose paren- 
chyma they are continuous. 
Typical parenchyma-tracheids occur in contact with this parenchyma, and 
with thick-walled copiously parenehyma-eells that have numerous simple 
pits (fig. 20). 
ec 
Medullary Rays. 
The uniseriate rays vary in height from 1-25 cells, while the fusiform 
rays vary from a height shorter than the highest uniseriate up to equal to 
30 cells. 
In the rays, apart from resinous epithelium, there are three kinds of cells : 
thick-walled and thin-walled parenchyma, also ray-tracheids. 
The thick-walled parenchyma-eells are much more abundant than the thin- 
walled. Each ceil is brick-shaped with a transverse or oblique terminal wall. 
The length equals the radial width of 6-8 tracheids in the spring-wood, and 
