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 O001 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 



