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 ^three 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 



