134 Brenchley . — On the Strength and Development of 
At first it is absolutely undifferentiated, but later on the cells at the peri- 
phery arrange themselves to form a definite surface layer. About a fort- 
night after pollination the first traces of differentiation can be made out ; 
towards the tip of the grain the cells in the middle begin to group them- 
selves into a central core, while lower down the initials of the cotyledons 
appear in the form of two slight projections on the dorsal side of 
the embryo away from the endosperm. These projections grow towards 
one another and eventually meet, closing round the inner mass of tissue 
which forms the rudimentary shoot and shows nuclei in active division ; in 
July 21 f 
July 26 ^ 
July 23^ 
fir 
July 291*1 
Text-fig. 4. Outline sketch showing development of plumule in grains pollinated on July 6, 
1907. c. cotyledon ; f.l. 1st leaf; s.l. 2nd leaf ; sc. scutellum ; a. axis of young shoot. T.S. x 62. 
about three days 5 time the edges of the cotyledon not only meet but fuse, 
so forming a kind of false tube, which, however, gives an indication of its 
real derivation in the fact that the two edges always remain free quite 
at the tip. 
Meanwhile the central core has become more clearly marked out, and 
about six days from its first appearance the young radicle begins to separate 
from the surrounding tissue, which forms the coleorhiza or root-sheath. 
Just at this time the first traces of the epiblast appear — the ligule which 
develops on the hypocotyl immediately above the radicle, on the dorsal 
side of the embryo. A little later the tissues of the radicle are seen 
