OF THE WOOD OF INDIAN SPECIES OF PINUS. 481 
B. Micnoscoric STRUCTURE. 
The interesting features in the microscopic structure of the wood are: 
There are unusually complete arrangements for the conduction of 
water in various directions in the body of the wood; for the 
tracheids may have bordered pits on all their walls. 
ii. Some of the tracheids assume unwonted forms. 
iii. The resin-ducts and associated parenchyma are very richly 
developed. 
Tracheids. 
In transverse section the spring-tracheids are wide and rectangular to 
hexagonal with the radial diameter exceeding the tangential. Passing 
outwards there is a very gradual shortening of the radial diameter, and 
thickening of the walls, until the outermost three or four rows of the summer- 
wood are flattened. The measurements are given below :— 
| SPRING-WOOD. SUMMER-WOOD. 
Radial. | Tangential. Radial. Tangential. 
| : 
Width of lumen .... |> 92u 194 
Thickness of wall.... 2u | 2 д m 5p 
Mean length of the tracheid 4:6 mm. 
In addition to tracheids of normal form, others occur with blunt rounded 
ende, and near the resin-ducts with transverse rectangular ends, also with 
feebly bilobed rounded ends. Here and there bundles of tracheids deviate 
from the straight course, portions of them run in a radial plane obliquely to 
the longitudinal axis, so that at spots not in contact with the medullary rays 
tangential longitudinal sections show transverse sections of tracheids (fig. 28). 
Where the ends of the tracheids abut upon medullary rays from above or 
below, some end bluntly, others bend and run radially transversely for shorter 
or longer distances and thus, so far as arrangement is concerned, form 
transitions between tracheids of the body of the wood and ray-tracheids. 
This transition is even more remarkably shown by those tracheids which bend 
into a medullary ray, so that their terminal portions run in a transverse 
radial direction and their terminal walls end direetly against a terminal wall 
