OF THE WOOD OF INDIAN SPECIES OF PINUS. 485 
lighter yellowish-brown spring-wood of the same annual ring. The pro-. 
portion between these two types of wood varies; in our specimen the 
summer-wood is about equal in quantity to the spring-wood, and is well 
| developed in most annual rings, so that the wood is rather hard and heavy. 
The resin-ducts are distinct in cross-section and more abundant in the 
summer-wood than in the spring-wood : they are marked as brown lines in 
longitudinal view. 
B. Microscopie STRUCTURE. 
Tracheids. 
In transverse section the spring-tracheids аге rectangular or feebly 
hexagonal, obleng, with the long axis radial. A marked feature of the spring- 
tracheids is the unusually large size of the lumina, associated with the 
moderate thickness of wall. This type of structure with radial elongation of 
the lumen persists throughout the spring-wood, and is correlated with the 
1-3-seriate arrangement of the bordered pits on the radial walls. In the 
inner stmmer-wood not only are the walls thicker, but also in transverse 
section the lumen is rounded and approximately isodiametric or slightly 
shorter in a radial direction. Тһе shortening of the radial diameter is most 
marked in the late summer-wood, so that the outermost two layers of 
tracheids have flattened lumina. 
The tracheids normally have typical rounded tips but occasionally show 
long tail-like continuations. On the medullary rays they terminate with 
blunt, flat ends or the terminal parts are bent, so that in extreme cases the 
curvature attains an angle of 180? ; thus in longitudinal tangential section 
transverse sections of these * wood-iracheids " are to be seen in contact with 
the medullary rays. 
One remarkable feature in this typical pine is the extraordinary length of 
the tracheids, which often attain 7 mm. in length. The mean dimensions of 
the tracheids are shown iin the succeeding table, and they show the very 
great size of the lumen of the spring-tracheids. 
SPRING-WOOD. OUTER SUMMER-WOOD. 
Radial. Tangential. Radial. | Tangential. 
Width of lumen ....) 685 д 45 р 10 pt | p 
| | 
Thickness of wall... | 4:9 р 4:9 и 6 | 8:9 p 
The structure of the radial walls and the arrangement of the bordered pits. 
