18 Campbell.—Studies on the Araceae. 
found in Aglaonema, but somewhat older ones were obtained 
in Lysic hi ton. 
The youngest embryo of Lysichiton which was found is 
shown in Fig. 33. The broad base of the embryo in this 
case, and the absence of the primary transverse walls, do not 
agree with the older stages, of which many were found, but 
resemble Hegelmaier’s figures of Pistia 1 , and also Hofmeister’s 
figure of the young embryo of Calla palustris. 
Stages like the one shown in Fig. 44 were frequently en¬ 
countered. Here the transverse segmentation of the basal 
region is still very evident; and probably the early divisions 
were like those in Aglaonema , and most Monocotyledons 
which have been investigated. There is, as yet, no differentia¬ 
tion of the primary organs of the embryo, which takes place 
very late in these plants. No suspensor is developed, nor is 
there any enlargement of the basal cell, which is so marked in 
many Monocotyledons—e. g. Alisma , A r aias, Lilaea , &c. In 
the absence of the suspensor, and the form of the embryo 
itself, these Aroids recall the Grasses, and also the embryo of 
Sparganium. The absence of a suspensor is clearly correlated 
with the complete investment of the young embryo by the 
endosperm, with which all of its superficial cells are in close 
contact, and from the cells of which they can abstract the 
substances necessary for the growth of the embryo. 
As the embryo enlarges it becomes somewhat flattened in 
the plane of the cotyledon. The first indication of external 
differentiation is the formation of a depression near the base, 
in the middle line of the cotyledon (Figs. 47, 48). This is the 
beginning of the stem-apex, but it is quite impossible to trace 
it back to the early segments of the embryo, which have 
become quite unrecognizable by this time. Probably the 
whole cotyledon (which comprises the greater part of the 
embryo), and the stem as well, are products of the terminal 
one of the three primary segments, but it is not possible to 
prove this positively. At this time the embryo is composed 
1 Hegelmaier, loc. cit. 
