164 BOTANICAL GAZETTE | MARCH 
the initial cell of the plerome with one of its segments being 
more deeply shaded). 
Thus it is seen that in very young embryos all the cells are 
meristematic, and no tissues are differentiated. The first tissue 
to differentiate is the dermatogen, the greater part of which is 
usually cut off immediately after the octant stage. Some time 
before the appearance of the cotyledons the dermatogen is com- 
pleted by a contribution from the suspensor. The periblem and 
plerome, which are indistinguishable at the apex and grow from 
a common meristem during the greater part of their intraseminal 
development, become completely differentiated and grow from 
separate initials before the intraseminal development is com- 
pleted. 
It must be remembered that the development of the primary 
root of an embryo, in which the suspensor usually plays such an 
important part, is a very different thing from the development 
of a lateral root which is not modified by any suspensor con- 
tribution. 
The suspensor presents some variation, as may be seen by 
comparing the figures of p/. XVZ. After the suspensor has reached 
the three or four-celled condition, which it does at a very early 
stage, its cells stop dividing until the dermatogen is cut off to 
complete the dermatogen of the root. The middle cells of 
the suspensor, 2. ¢., the one or two cells below the hypophysis, 
then divide and sometimes give rise to eight or ten cells. The 
suspensor cell nearer the micropyle does not seem to divide. 
A glance at such embryos as those represented in figs. 77 
and 73 will show that the development below the first transverse 
division of the. embryo is more ar and symmetrical than 
that of the upper half. In the hypocotyledonary portion 
there is a zone of cells (2, figs. 714, 73) which is frequently quite 
conspicuous at sip since Below — zone son same figures show 
that the ar 1. Even in the 
upper part, an 1 embryo as ‘regular as that. drawn in fig. 71 shows” 
some emery in oe er bell = heets, a ey there 
is nol I loutline. Ihave © 
; = Res nrema NE a | Ber” Ss r : oS 
