466 DR. Р. GROOM AND MR. W. RUSHTON ON THE STRUCTURE 
(h) Other Structural Features of the Tracheids. 
As regards the thickness of tracheid-wall and size of lumen the transition 
form spring-wood to autumn-wood is, as would be anticipated, gradual in the 
haploxylie P. excelsa and P. Gerardiana, and more sudden in the diploxylie 
P. longifolia and P. Merkusii, but unexpectedly is gradual in the diploxylic 
P. Khasya. As seen in radial section the walls of the tracheids are very 
clearly thicker, against the medullary rays than elsewhere. 
Radial lignified bars, ** Sanio’s bars" stretching across the lumina of a 
series of tracheids were seen in several of the species. The bars seen in 
transverse section were hollow, and mostly eylindrieal, but close to the 
attachment to the tracheid-wall the bar may deepen so that the contours of it 
and its cavity are vertically elongated (РІ. 24, fig. 22). 
* Resin-plates ? occur in some of the Indian pines, e. 
g, P. excelsa. 
(i) Resin-Ducts 
In all the Indian pines except P. Gerardiana the resin-ducts are most 
abundant in the outer part of the annual ring, but in that species they are 
most numerous in the middle part of the ring and are unusually uneven in 
distribution, being locally scanty. 
P. longifolia and P. Khasya are marked by great development of the 
ducts ; in the former the ducts are very wide (diameter *2 mm.), and solitary 
or in pairs, mostly in the outer and middle parts of the annual ring. 
P. Khasya has very numerous ducts ranged usually in groups of 2-4. 
The species show the following types of cells associated with the ducts 
(figs. 2, 20, 31, 42). 
(1.) Thin-walled epithelium lining the duct. 
Gi.) Thin-walled, more elongated parenchyma. 
(11.) Thick-walled, still more elongated parenchyma, the walls of which 
bear numerous simple pits. 
(iv.) Parenchyma-tracheids, much shorter than ordinary tracheids, 
with bordered pits on all their walls, including the terminal 
transverse walls. 
(k) Medullary Rays. 
Except in P. excelsa thin-walled parenchyma, as well as thick-walled, occurs 
in the medullary rays. This species has only the latter. 
In all Indian pines ray-tracheids, both marginal and internal (so-called 
“ interspersed ”), occur. In the haploxylic species P. exeelsa and P. Ger- 
ardiana the ray-tracheids bear no denticulations on their walls, or in the 
latter species such denticulations are scantily and feebly suggested. The 
three diploxylic species all have denticulate ray-tracheids. 
