Campbell.—Studies on the Araceae . 19 
of apparently homogeneous tissue, and it is not until a late 
period that the vascular bundles are evident. 
As the embryo enlarges it becomes somewhat heart-shaped 
(Fig. 50 a , b), and near the base of the cotyledon there can be 
seen for a short distance a strand of procambium. The stem- 
cleft has become deeper, but is almost completely enclosed 
by the base of the cotyledon which forms a sheath about 
it. Up to this time, no certain evidence of the primary root 
can be traced, and it is evidently very late in making its 
appearance. 
Fig. 52 shows a median section, at right angles to the 
plane of the cotyledon, of a nearly full-grown embryo. The 
young vascular bundles could be seen, although they were 
very slightly developed. Within the cleft at the base of the 
cotyledon is the protuberance which probably represented 
not only the stem-apex, but also the beginning of the second 
leaf. A short branch of the bundle of the cotyledon runs 
into this stem-rudiment (or leaf?), and a larger branch is 
continued obliquely into the rudiment of the root (r.), which 
is very evidently of lateral origin, and shows no very clear 
arrangement of the tissues. 
Fig. 55 shows two sections of a full-grown embryo of 
Anthurium cordifolium , which in the main agrees with that 
of Lysichiton , but the stem-apex is higher up, and the root,, 
which is much better developed, is terminal, as it is in most 
investigated Monocotyledons. 
It is evident that, among the Araceae, the development 
of the embryo shows a good deal of variation, and more 
information regarding the early divisions of the embryo is 
much needed. If the early stages shown in Aglaonema are 
normal, there are two well-marked types at least—that where 
the embryo first becomes divided into two transverse seg¬ 
ments, and that in which there is a more or less regular 
quadrant-formation, as in Pistia , and in the very small number 
of young embryos found in Lysichiton. Most of the older 
embryos seen in the latter, however, point to an early seg¬ 
mentation like that in Aglaonema. 
