



THE WOOD. 
wide (fig. 7 c, p. r., and fig. 11), while others which contain resin 
canals are from 4 to 6 cells wide (fig. 12). In radial sections these 
rays are cut longitudinally (fig. 7 b, p. vs.), and 
are made up of two kinds of cells. Figure 5 
shows the character of an ordinary pith ray 8 
cells high. The cells in the upper row and those 
in the lower two rows (fig. 10, 7. ¢.) are ray tra- 
cheids. These have teeth-lke projections on 
their upper and lower walls, and bordered pits 
both in their side and end walls, characters which 
distinguish ray tracheids from the next inner 
row of cells (parenchyma cells), the latter hav- 
ing thick walls and large 
simple pits (fig. 10, s. p.) 
on the inside walls. There 
are from 1 to 5 simple pits 
within the width of each 
vertical tracheid (fig. 10,7.). 
The end walls of these pa- 
renchyma cells are thin or 
sometimes locally thickened 
(fig. 10, ¢. w.). Other pa- 
renchyma cells, with thin, 
smooth, entire, upper and 
lower walls, and partly ab- 
sorbed cross walls, occur 
within the pith rays (fig. 
39 




_--4p 


Cras 



re. | 
RADIAL Ea 
ex 
aay 
Root 


Fig. 11.—An ordinary 
pith ray as viewed in 
a tangential section 
magnified 300 diam- 
eters; a, walls of 
adjoining tracheids; 
r.t.. ray tracheids; 
mGp Tay Cells: 0 aps. 
bordered pits. 

12.—A 
containing a 
duct, vr. d., magnified 
300 diameters; r. t., 
Fie. pith ray 
resin 
ray tracheids; r. ¢., 
ray cells; ep. ¢., epi- 
thelial cells; 0b. p., 
bordered pits. 

10, c.). These parenchyma 
cells have small elliptical or oval pits (fig. 10, 
s. p.), from 1 to 4 of which usually occur within 
the width of each tracheid. 
Transverse sections of the two forms of pith 
rays just described, as they appear in a tangen- 
tial section of the wood, are shown in figures 6 
and 7. The ordinary pith ray shows 3 ray tra- 
cheids (fig. 11, 7. ¢.) above and 2 below. The 
5 thick-walled elements (fig. 11, 7. ¢.) in the 
middle of the ray are pith ray parenchyma cells. 
The form of pith ray containing a resin duct 
(fig. 12) presents the same details of structure 
as the ordinary ray, with the addition of epi- 
thelial or resin-secreting cells (fig. 12, ep. c.) 
which line the resin duct (fig. 12, 7. d.). The 
upper and lower rows of cells (fig. 12, 7. ¢.) are ray tracheids, corre- 
sponding to those pointed out in the ordinary pith ray (fig. 11, 7 ¢.). 

