OF THE WOOD OF INDIAN SPECIES OF PINUS. 479 
9-10 in the summer-wood. All the walls are pitted. On the lateral (radial) 
walls the pits are of moderate size but not nearly equalling the height of 
the cell ; they are arranged in one or two horizontal series, with 1-3 pits in 
each series. The outline of the pitis usually very broadly lenticular, with the 
long axis nearly horizontal or oblique, or nearly circular, but the thickening 
on the two sides is not exactly similar, so that the pits often show a double 
outline, the aperture or area being often slightly narrower on the tracheid- 
side (fig. 24). This distinction is more marked in the summer-wood where 
the orifice on the tracheid side is narrowly fusiform and nearly erect, and in 
a vertical direction often longer than the diameter of the chamber, while on 
the side away from the tracheid the pit oritice is shaped as in the spring- 
wood (fig. 22). The terminal walls have coarse reticulate thickenings, so 
that oval, fusiform, or cireular pits result. In tangential section, the cell- 
Jumen is mostly oval with the long axis erect in uniseriate rays (fig. 25), but 
more rounded in fusiform rays. They do not bulge into the adjoining 
tracheids like thyloses. 
The thin-walled parenchyma-cells have unpitted terminal walls, which are 
transverse and bow-like. Towards the tracheid on the radial walls their 
pits often resemble those of the thick-walled parenchyma, but often are 
so much larger that in the spring-wood there may be only one pit to the 
radial width of a tracheid, and this one pit stretches across the whole height 
of the parenchyma-cell. In the summer-wood the slit-like orifice is often 
longer that the circular chamber. The upper and lower walls are not pitted. 
The occurrence of large pits and relatively small bordered pits on the radial 
walls of ray-parenchyma of one and the same pine, is of special interest in 
relation to the classification of the genus and the systematic position of 
P. longifolia. 
The ray-tracheids show bordered pits on all walls. The walls of the mar- 
ginal tracheids bear denticulations, which sometimes nearly meet across the 
lumen and are more pronounced in the summer-wood than in the spring- 
wood. The terminal walls are transverse or oblique. Internal ray-tracheids 
oceur and have curved terminal walls; some are unusually wide and others 
narrow. 
The wniseriate rays are usually composed of thick-walled parenchyma 
(fig. 25) with or without rav-tracheids, but in some cases thin-walled 
parenchyma forms a considerable part of the ray. Where the ray crosses 
a resin-duct, thick-walled, starch-containing parenchyma is often but not 
always replaced by thin-walled, slender brick-shaped cells with more elon- 
gated pits on the side walls and entire transverse walls, Neither are ray- 
tracheids always replaced across the duct by parenchyma, for very slender 
ray-tracheids are to be seen crossing the duct. 
Here and there occur rays that are bisertate in the middle and uniseriate at 
the margins, and are devoid of resin-duets. 
