8 MR. W. RUSHTON : STRUCTURE OF THE 
wood, and the rest to the spring. In outline they are square to round in the 
spring and oblong in the summer wood. When isolated they show a length 
ofj2-3 mm., with width of lumen and thickness of walls as follows :— 
Width of lumen. Thickness of wall. 
Radial. ‘Tangential. Radial. Tangential. 
Spring wood ......... 29 u 23 p 1'4 р 14 u 
Summer wood ...... Ти 2w 2 س‎ 2p 
The ends of the tracheids in most cases are rounded off, sometimes forked 
and flattened where they end on a medullary ray, and occasionally bend and 
run along the ray-cells as in J. recurva. 
The bordered pits оп the radial walls are arranged in a single series with 
occasional pairs, but are more numerous and closer together than in 
J, recurva. They are round, with a circular orifice in the early spring wood 
which gradually becomes lenticular as the summer wood is reached (fig. 16). 
Pits also occur on the tangential walls of the summer wood ; these have 
lens-shaped openings like those on the radial walls (fig. 17). 
Sanio's bars occur very frequently together with Sanio's rims above and 
below the pit-areas; they can be demonstrated in both radial and tangential 
sections (figs. 18, 18а). 
Medullary Rays. 
These are numerous and wide, occurring at a distance of 1-12 tracheids 
away from each other tangentially and made up entirely of. thick-walled 
parenchyma, with a length equal to the width of 4-8 tracheids in the spring 
wood and 3-6 in the summer, with simple pits on the upper and lower walls, 
1-4 half-bordered pits per wood-tracheid on the lateral walls, and numerous 
irregular-shaped simple pits on the end-walls. Оп the lateral walls the pits 
are round, with orifices slit-like, slightly wider in the middle, and rarely 
extending beyond the border (fig. 19). 
Tangentially the rays are mostly uniseriate (fig. 20), 1-18 cells high, with 
occasional biseriate ones (fig. 21); the cells are round in the middle and 
oblong above and below, and often loosely attached to each other, so that 
intercellular spaces can be seen in both radial and tangential sections. АП 
the rays are more or less resinous. 
Resin Cells. 
The resin cells occur in a zonate manner in the late spring and early 
summer wood, and never occur beyond the fourth row of tracheids from the 
outer limit of the growth-ring, but occasionally they are scattered, especially 
in rings which happen to be rather wide. 
