26 
WRIGHT: THE GENUS DIOSPYROS 
transverse sections only differ from the vessels in being 
usually of smaller diameter. They are generally limited to 
the neighbourhood of large vessels, frequently flanking 
the tangential surface, but in D. Embryopteris they may 
occasionally be seen among fibres. 
The transverse dimensions are often only a trifle in excess 
of the largest wood parenchyma cells, but in some instances 
they attain a radial diameter of 0*04 to 0*08 mm. In length 
they come next to the fibres and may attain 0*27 to 0*90 mm. 
When of great length the ends taper very strongly, and in 
such cases it is difficult to distinguish them from the more 
abundant fibres, and the term “ fibre-tracheids ” would be 
very appropriate. The commonly small and constant trans¬ 
verse dimensions of true fibres seems to differentiate them 
from tracheids, but otherwise it often becomes well nigh 
impossible to distinguish a short fibre from a narrow lumined, 
long tracheid. 
Parenchymatous Elements. 
This includes the wood parenchyma, fibres, and medullary 
rays of the secondary xylem. It is in the distribution of 
these elements that the maximum variation occurs, and even 
in our Ceylon species it is sufficient to allow of a grouping 
of the species into sections according to— 
(1) Whether the medullary rays are one cell in tangential 
breadth. 
(2) Whether the medullary rays are more than one cell 
in tangential breadth. 
(3) The presence of special radial groups of parenchyma. 
As with the tracheal elements, the general features of 
distribution, histology, and function may be subject to all 
manner of variation according to the internal and external 
forces at work. 
The parenchymatous tissues compose the greater part of 
the secondary xylem and increase considerably with the age 
of the cambium. It is obvious that the value of the timber 
