16 ARISAEMA TRIPHYLLUM 
detail. Growth takes place by a division of all the cells of the 
embryo, resulting in the formation of a symmetrical, globular 
body (TEXT FIGS. 15, 16,18). TEXT FIG. 20 shows a cross section 
of such an embryo as is shown in longitudinal section in TEXT 
FIG. 16. At this stage there is no differentiation other than the 
formation of a distinct epidermal layer. The form soon changes 
from globular to ovoid and then tends toward cylindrical. During 
these changes two growing regions develop. The distal portion 
develops the cylindrical cotyledon while a lateral protuberance 
shows the initials of the plumule (TExT FIGS. 13, 14). The coty- 
ledon continues growth both in length and width much more 
rapidly than the plumule and finally 
surrounds the latter almost entirely 
(TEXT FIG. 23 B). 
The mature embryo is 1-1.5 mm. in 
length and approximately one fourth as 
thick. It is cylindrical or ellipsoidal in 
form, attached to the endosperm periph- 
ery by the hardened suspensor cells at 
the radicle extermity, and lying in a 
cavity lined by the collapsed endo- 
sperm cells from which the food ma- 
terial has been absorbed. It shows 
clearly marked dermatogen, periblem 
and plerome areas below the plu- 
mule, with a well developed calyptrogen 
Fic. 22, Reconstructed and cap as in a normal root. The 
Vascular system for mature j 
eikbryo. (XX JK plumule shows one leaf enveloping a 
FIG. 23A. ees stem initial group wholly or nearly so 
cr©ss section of FIG. 22 at A. (TEXT FIGS. 22, 23B). The vascular 
T e Diagrammatic system of the embryo shows only funda- 
cr@ss section $ FIG. 22 at B., 
DP. de ED; branches mental elements—largely protophloem, 
of aes strand. L’, L”, and consists of a cylinder in the radicle 
ce and forward lateral with six primary branches just below the 
plumule (TEXT FIGS. 22, 23A). The 
largest or dorsal strand with two laterals produced at about the 
level of the plumule tip extends almost to the extreme tip of the 
cotyledon. There are two lateral pairs of branches, one in the 
