INTRODUCTION ' 15 
(iv) The medullary rays (vide fig. 67) are composed of 
two kinds of cells. Firstly, the medullary ray parenchyma 
cells with thickened, cellulose, or slightly lignified, walls 
with 2-5 (generally 4) slit-shaped simple pits into each 
tracheide they cross. These cells contain protoplasm, 
nuclei, starch, and resin. And, secondly, mcdullary ray 
tracheides which are not present in all rays, but are present 
on the upper and lower sides of many of them, and occur 
as intermediate layers of some. These cells have thin 
lignified walls with small bordered pits, and contain only 
water. 
Medulla. This is the star-shaped central portion, having 
usually five unequal points which are left by the tracks of 
leaf traces, and thus correspond to the five rows of leaves. 
The medullary cells have at first cellulose walls, but when 
secondary wood is formed they become lignified, though 
the cells may still contain starch. 
