OF THE WOOD OF INDIAN SPECIES OF PINUS. 475 
Apart from the resin-producing epithelium the parenchyma shows two 
extreme forms, and ray-tracheids occur, Some of the uniseriate rays are 
composed solely of ray-tracheids. 
In particular some rays, so-called “distended rays,” consist solely of 
a line of ray-tracheids of characteristic shape. Та such rays each tracheid 
on the radially inner end is blunt or tapers to a more or less fine point, 
it widens in an outward direction and divides at its widest region into 
two or three marked lobes arranged in a vertical plane. In the ease of 
two-lobed tracheids, the ends of the next tracheid dovetails with the two 
lobes ; in the case of the three-lobed tracheids, the medium lobe may be 
continuous with the beginning of the next ray-tracheid, or the successive 
Tay-traeheids are not in contact (fig. 10). More or less similar ray-tracheids 
occur marginally on other uniseriate rays that include parenchyma (fig. 11), 
In normal rays the ray-tracheids are mainly marginal though internal 
ray-tracheids do occur, and their radial continuity is sometimes disturbed by 
the intercalation of ray-parenehyma. Sometimes there occur very long 
slender ray-tracheids whose lumen locally is reduced to a thin line (fig. 12). 
The ray-tracheids show bordered pits on all their walls, and are devoid of 
denticulations. 
The ray-purenchyma is composed of rather thick-walled cells elongated 
radially and having simple pits on all their walls. On the radial walls the 
typical broader ones have large oval pits elongated radially ; in the spring- 
"wood to the radial width of one wool-tracheid there is one pit, which nearly 
stretches across the whole height of the cell, or occasionally two or three 
pits: when there are three the pits are in two tiers (fig. 9). In the summer- 
wood there 1s still one pit to the radial width of each tracheid, but the pit 
area is fusiform and steeply oblique towards the lumen and slit-like towards 
a tracheid. The end wall bears a few large pits, so that it belongs to 
Penhallow’s “locally thickened type." The other parenchyma-cells are 
usually shallower, their pits are smaller and more crowded together so that 
the thiek portions of the wall form bars which are linked to form a 
reticulum, These latter cells appear to be specially numerous close to the 
resin-duets of the wood of the medullary ray. The parenchyma-cells often 
bulge into the lumen of the contiguous tracheid to form thyloses (fig. 17) 
(їп sections the pit-closing membranes often also dip into the cavity of the 
parenchyma-cell itself). 
In the fusiform rays the resin-duct is walled by a flattened epithelium 
(whose cells in our specimen had produced many thyloses). Surrounding 
this are thin-walled parenchymatous cells elongated radially (in our speci- 
men on the flanks of the ray these were very much flattened as if crushed). 
Above and below in tangential section occur two or three tiers of triseriate 
‚ог biseriate thick-walled parenchyma-cells, which in turn are succeeded by 
А 2х2 
