IN CEYLON. 
31 
These elements form large patches of tissue, often entirely 
tilling the gap between adjacent medullary rays ; at other 
times scattered with intervening wood parenchyma. In the 
heartwood the fibres form much larger and more compact 
areas, in radial and tangential thickness. In the sapwood 
one meets with relatively narrow bands of fibres, often only 
a single radial line of fibres existing between adjacent 
medullary rays. 
In their vertical distribution one notes the wavy outline of 
individual fibres and the deviation from the vertical of their 
tapering ends. 
The fibres are mainly in contact with like elements, or 
with those of the wood parenchyma on their tangential 
surfaces and medullary ray cells on their radial surfaces ; 
they are rarely in direct contact with vessels, since the 
latter are usually surrounded by short parenchyma cells. 
There is nothing remarkable in their form ; they possess 
the normal thick or thin walls, small transverse dimensions, 
great vertical length, and strongly pointed ends. 
The transverse outline is usually strikingly angular, and 
the lumina may be only partially or almost completely closed 
by the secondary thickening of the walls. As previously 
mentioned, the vertical outline is often wavy and deviates 
considerably from the vertical near the tapering ends. 
The constancy in transverse dimensions is exhibited in 
these elements better than in any others ; the maximum 
variation is however seen in the length of these elements, 
since they vary from that of a cambium cell to over 1 mm. 
in length. The thickness of the wall varies from 0*001 to 
0*003 mm. 
The range of variation in transverse dimensions as one 
passes from the heartwood to the sapwood in very old trees 
is very small, and this relative constancy allows one to readily 
distinguish the scattered fibres from other elements. A list 
