22 Campbell. — The Development of the Flower and 
tell whether it is derived from cells originating from the 
terminal segment of the embryo, or from the segment im- 
mediately below, as at this time the limits of the original 
segments can no longer be recognized with certainty. From 
its strictly lateral origin, however, and a comparison with 
other forms where the origin of the stem-apex is undoubtedly 
from the second segment, it is probable that in Lilaea the 
terminal segment gives rise to the cotyledon only, and that 
the stem is the product of the next segment. 
The rapid increase in size in the embryo which now takes 
place is mainly due to the growth of the cotyledon, while 
the lower part of the embryo remains short. In the cotyledon 
the plerome-strand is easily seen (Fig. 41), but it is much less 
evident in the basal part of the embryo. The epidermis is 
well defined in all parts of the embryo. 
In cross-sections of the older embryo made through the 
region of the stem-apex, the latter is seen lying in a shallow 
indentation formed by the base of the cotyledon, whose 
margins are beginning to form the sheath which later com- 
pletely encloses it. 
The point in which the embryo of Lilaea differs most 
markedly from that of other Monocotyledons which have 
been examined, is the origin of the primary root. This, 
instead of lying with the apex in direct contact with the 
suspensor, is decidedly lateral in position. In the earlier 
stages of the embryo it is impossible to make out clearly the 
relation of the tissues of the root to the other parts of the 
embryo. As soon as the root can be recognized as such, its 
axis is almost coincident with that of the stem (Figs. 41-43), 
and forms a marked angle with that of the cotyledon. It 
was not possible to decide positively, from the sections which 
were examined, what was the exact origin of the different 
root-tissues. The plerome is evidently continuous with the 
original axial plerome-cylinder of the young embryo, and is 
probably derived from the central cells of the second, and 
perhaps the third segment ; i. e. it is derived, in part at least, 
from the same segment as the stem. In the older embryo 
