IN CEYLON. 
27 
is greatly due to the percentage composition of elements of 
the parenchyma type and the structure and form of these 
elements. 
In the poorer timbers the wood parenchyma is usually of 
the thin walled, wide lumined type, and this alone is often 
responsible for the inferior quality, for no matter how thick 
and long the surrounding fibres may be, the soft bands 
of parenchyma, when present, lead to early cracking and 
decay. 
Wood Parenchyma .—In transverse sections the presence 
of these elements is usually determined by the abundance 
of carbohydrate and mineral contents, together with their 
relatively thin walls and wide lumina. Often, however, they 
are not easily distinguishable, sometimes because their trans¬ 
verse dimensions are similar to those of the neighbouring 
cells, as in D. quæsita ; sometimes on account of the 
proximity of adjacent medullary rays, and again because the 
surrounding fibres may not have undergone much lignifica¬ 
tion ; the latter is often the case in the secondary xylem of 
young twigs. In some species they are always very 
conspicuous, either on account of their lumina being very 
large, or because adjacent medullary rays are separated by 
patches of fibre of considerable tangential width. 
The difficulty of distinguishing these elements, however, 
is only when one is limited to transverse sections ; the great 
length of these elements and their numerous contents serve 
to isolate them in any longitudinal section. 
The distribution of these elements is somewhat complex, 
and is such that a continuous system of elements of the 
parenchyma type is established, together with frequent direct 
and indirect contact with the tracheal elements. The wood 
parenchyma cells are distributed as tangential bands, oblique 
bands, and around large tracheal elements. The tangential 
bands usually extend from one medullary ray to another, 
and their significance varies according to the width of this 
gap ; the tangential bands between adjacent rays in xylem of 
