OF THE WOOD OF INDIAN SPECIES OF PINUS. 473 
and uniseriate towards the margins, are mainly eomposed of thick-walled 
parenchyma, with one or two tiers of marginal rav-tracheids. 
Hence apart from or surrounding the resin-ducts, both types of rays are 
composed of thick-walled parenchyma, with a smaller number of marginal 
ray-tracheids, together with sporadic thin-walled parenchyma and internal 
ray-tracheids. 
PINUS EXCELSA, Wall. 
This five-needled species belongs distinctly to the temperate climate, as its 
range of altitude in the Himalayas is from 6,000 to 12,000 ft. Its area 
stretches from Afghanistan to Bhutan. 
As this species is widely grown in Europe the appearance of the wood is 
familiar, but for the sake of completeness a brief description of the structure 
of this is given. 
A. Macroscopic FEATURES (naked eye). 
The wood is light in colour, the sapwood being whitish and the heartwood 
a light red. In each annual ring the spring-wood gradually merges into the 
summer-wood with no sudden transition, The annual rings vary in width from 
1 to about 21, or less, of an inch (in our Indian specimen the mean thickness 
was уу of an inch). The medullary rays are visible to the naked eye as 
yellow lines in the heart-wood.  Resin-duets are numerous in the outermost 
spring-wood and especially in the summer-wood. 
D. Microscopic STRUCTURE. 
Tracheids. 
Spring-wood formed the greater part of the annual rings in our specimen : 
for instance, in one ring the radial row of tracheids was constituted of 28-30 
forming the spring-wood, and 5-8 forming the summer-wood. In transverse 
section the inner spring-tracheids are mostly square or rectangular-oblong 
with a longer radial diameter. The transition to summer-tracheids is very 
gradual, and only a few of the outermost of these show marked shortening 
of the radial diameter. Below are given measurements of typical tracheids, 
whose length is 3-4-4 mm. 
| | Width of Lumen. Thickness of Wall. 
| Radial. Tangential. Radial. | Tangential. 
| Spring-tracheids . | 385 p Oron | Sty | ЗЯ 
| | | | 
| Summer-tracheids. E Il 5n | 285pn | 44и | 44и | 
LINN. JOURN,— BOTANY, VOL. XLI. 2N 
