22 
WRIGHT : THE GENUS DIOSPYROS 
and when sufficiently thin the section is removed and 
finally polished on a razor stone. This method allows one 
to obtain fairly large sections, though smaller sections cut 
by hand in the ordinary way provide ample material for 
obtaining all points in detail. 
Histology of the Timbers .—The anatomy of the secondary 
xylem of the Ceylon species of Diospyros is of the ordinary 
arborescent dicotyledonous type. The differentiation of the 
tracheal elements and fibres is remarkably uniform, but 
the parenchymatous tissues exhibit sufficient variation to 
allow of a grouping of the various species under different 
types. In dealing with the distribution, size, form, and 
percentage number of the secondary xylem elements one 
must allow for variability even for members of the same 
species, since they may have developed under quite dis¬ 
similar climates and their internal requirements are probably 
at great variance. As far as possible the statements have 
been made in a general sense, and where it has been possible 
to obtain material of the same species in the dry, wet, and 
intermediate zones, this has been done. 
Tracheal Elements. 
The tracheal elements are almost wholly represented by 
vessels ; tracheids are never abundant, and when present 
usually occur alongside a large vessel. 
Vessels .—The distribution of these elements varies accord¬ 
ing to the species, the age of the secondary xylem, and the 
climatic conditions under which the plants have grown. 
Usually the vessels occur in a more grouped condition in the 
xylem of the first few years than in the sapwood of old 
trees. 
In some species the heartwood appears to be characterized 
by an equal number of isolated vessels and radial groups of 
two or Uiree cells. Usually the members of vessels, when 
occurring in groups, form rows two to four cells in radial 
thickness ; in others, notably D. attenuata, the groups may 
contain twenty members arranged one to two cells in 
