482 DH. P. GROOM AND МК. W. RUSHTON ON THE STRUCTURE 
of a ray-tracheid (fig. 24). Other tracheids push their ends between the 
ау cells, so that in tangential section such tracheids may be seen cut 
transversely. 
The bordered pits are mainly on the radial walls. In. the wider spring- 
tracheids they are uniseriate or biseriate with circular apertures (fig. 35). 
The biseriate pits are circular in outline or slightly flattened where the pits 
are in lateral contact. The chambers of the uniseriate pits are often 
elliptical in contour with the long axis transverse. In the narrow summer- 
tracheids the radial pits are much seantier, uniseriate, and have oblique 
narrow fusiform apertures (fig. 36). 
In addition to the bordered pits on the radial walls there are others on the 
oblique lateral walis of tracheids that are hexagonal and pentagonal in trans- 
verse section, and on tangential walls of some tracheids (fig. 30). These 
tangential pits occur in the first place on tracheids that are contiguous with 
the parenchyma on the radially inner and outer sides of the resin-ducts. 
Tangential pits also oceur often, if not. exclusively, in the bundles of bent 
tracheids already described, especially or solely near the ends of the obliquely 
directed portions, Here they are most abundant in the spring-wood though 
not absent from the summer-wood, Inasmuch as these bent tracheids form 
radial series and their bent ends are often at approximately the same level, in 
transverse sections the tangential pits are seen in radial rows. The occurrence 
of bordered pits on the tangential walls of species of Pinus that usually have 
none has been recorded (see Strasburger), but in such cases the tangential 
pits appear to be characteristic of unusually narrow annual rings, whereas in 
Pinus Khasya these radial bands of tracheids with tangential pits oecur in 
wide annual rings. 
Finally, bordered pits occur on the transverse or bluntly rounded walls of 
the same types of tracheids that have tangential pits, as well as on tracheids 
that end bluntly against ray-tracheids (fig. 29). 
Sanio’s rims are distinct in the spring-wood (fig. 35). 
As seen in the radial section, the walls of the tracheids in contact with the 
medullary rays are thicker than elsewhere, as in the case with resin-tracheids 
of Dammara. As there is no question of resin-tracheids here, the thickening 
of the wall in Mammara may be connected with the proximity to the 
medullary ray and not with the existence of resin-plates, 
Resin-Ducts. 
The resin-ducts are most numerous in the outer half of the annual ring, 
where they tend to form a tangential series as seen in transverse section. 
Very few isolated ducts oceur at the inner boundary of the annual ring. 
Outside this zone succeeds a spring-zone devoid of ducts. 
