66 WRIGHT : THE GENUS DIOSPYROS 
advanced in the median cotyledonary trace as compared with 
the laterals. 
In the short axis of the embryo it is difficult to fix on the 
exact area at which lignification first appears. Examination 
of later stages shows the maximum lignification of the coty¬ 
ledonary xylem at the collet area, and that the lignification 
subsequently spreads downwards into the primary root and 
upwards into the hypocotyl. The collet area is also the first 
to show a vascular cambium and the maximum parenchy¬ 
matous system ; it therefore appears to be the centre of 
activity of the seedling axis. 
The fact that the lignification of the cotyledonary xylem 
reaches the maximum at the collet area may, however, still 
allow of the original starting point being at the cotyledonary 
node, and the enhanced lignification at the collet may be a 
secondary development associated with the requirements of 
the seedling subsequent to the purely embryonic stage. In 
the embryo the conducting systems are functioning in the 
conveyance of nutritive materials from the endosperm to the 
primary axis, and there does not therefore appear to be any 
necessity for lignification to commence at the collet area. 
There is the possibility that the direction of lignification 
may be purely responsive to the requirements of the 
seedlings, in which case no evidence can be obtained of 
the direction of differentiation of the original xylem 
elements. 
The lignification is completed throughout the hypocotyl 
and primary root of the embryo within such a period, that 
prior to the apex of the primary root presenting itself at the 
micropyle a continuous series of lignified elements exist 
from root to cotyledons. 
The epicotyledonary strands when present in the primary 
root show a definite direction of differentiation. 
The phloem of each epicotyledonary strand begins at the 
epicotyl leaf and spreads downwards into the hypocotyl and 
root. This direction of differentiation is obviously the best, 
