484 DR. P. GROOM AND MR, W. RUSHTON ON THE STRUCTURE 
tracheid gradually narrows and its long axis is increasingly erect (fig. 37) : 
while the aperture and contour on the side of the wall truly belonging to the 
parenchyma-cell remains broad, fusiform or nearly circular. Occasionally 
the pit-membrane bulges into the contiguous wood-tracheid. The terminal 
and upper and lower walls are devoid of pits. In tangential section the cells 
are, in the uniseriate rays, mostly vertically elongated, being oval-oblong, but 
more rounded in the fusiform rays. 
Parenchyma-cells with slightly thicker walls occur, They differ from the 
thin-walled cells also in the occasional occurrence of pits in the terminal, 
upper, and lower walls. 
the vniseriate rays show marginal and internal ray-tracheids, which may 
be replaced by parenchyma when crossing a resin-duct. The proportion of 
parenchyma and ray-tracheids varies. Some low rays are composed entirely 
of ray-tracheids ; in taller rays, too, ray-tracheids may  preponderate 
(fig. 2). 
The fusiform rays include a small resin-duet which is the central or nearer 
to the upper or the lower margin. Outside the epithelium is a somewhat 
similar layer of flattened thin-walled parenchyma, which here and there is 
interrupted by flattened cells which have thick lignified walls on the side 
distant from the epithelium. Above and below this tissue the ray is two cells 
in thickness, but there are only two biseriate layers of cells, which are 
parenchymatous, either thick-walled or thin-walled. Elsewhere the ray is 
uniseriate and composed of parenchyma and marginal and internal ray- 
tracheids (fig. 33). 
PINUS MERKUSII, Jungh. у de Vriese. 
In habitat this two-needled species is the most tropical in Asia, as it occurs 
in the Philippines and Cochin China, and stretches from Burma southwards 
to the Malay Peninsula, at altitades varying from 300 to 3,500 feet, and 
reappears in Sumatra. As regards supply of moisture the tree appears to be 
capable of enduring considerable dryness, for it is found in hot dry forests | 
on the Shan Hills, but judging from its distribution elsewhere the species 
also flourishes on sites where at least atmospheric moisture is abundant. 
The bark is thick. 
A. Macroscoric FEATURES (naked eye). 
The yellowish-brown heart-wood shows very sharply marked annual rings, 
of which there were about eighteen to the inch radius in our specimen, and 
eleven in the specimens mentioned by Gamble. Thus, in spite of the tropical 
distribution, growth in thickness appears to be comparatively slow. The 
reddish-brown summer-wood is sharply and suddenly marked off from the 
