WRIGHT : THE GENUS DIOSPYROS 
to give a systematic value to the H percentage composition of 
the xylem. 
Change in Percentage Number of Elements in Old and 
Young Xylem.— In every species the percentage number of 
tracheal elements decreases with the age of the cambium, the 
first formed xylem having the maximum percentage number 
and the last formed the minimum. The number of tracheal 
elements in the heartwood may reach 3*43 per cent, as in D. 
insignis, or be as low as 0*8 per cent, as in some specimens 
of D.sylvatica; this is a very low number, but in the sap wood 
it is still lower, the maximum being 1*4 per cent, in D. ovali- 
folia and D. montana and the minimum 0*3 per cent, in D. 
affinis. 
Hence we see that the percentage number of tracheal 
elements in young and old xylem of all onr Ceylon species 
does not vary more than S per cent., and the relatively low 
percentage number will serve to systematically diagnose the 
secondary xylem of onr species of Diospyros. The tracheal 
elements are represented bya lower percentage number than 
cmLl IT k PareBChyma this is to b- 
i'ssrissirsrs: 
instance D. acuta with 0*4 uer o a tw ’ 38 f ° r 
per cent. The thinnest ,2*. ^ n 
montana, with a percentage number of 14 in the rapwood 
moist, is D. attenuate with a OCTcem a<ld **“ 18 alwayB 
sapwood of stems 140 nun. diaJet^T r ° f °® “ ^ 
Though knowledge of the individual variation. 
t0 ■ tan,r 
specie, growing in the wet lll! " 0te in 
“ —- 18 ? 
