STUDIES OF THE DEVELOPMENT OF PEPEROMIA HISPIDULA 363 
become distorted and shriveled. This layer is clearly the chief 
protective layer of the seed. Near the base of the ovule the cells 
of the two or three layers of the integument may become thickened 
and brown (fig. 108). Across the base of the nucellus a series of 
5 or 6 layers of transversely expanded cells become thickened, and 
thus serve as a protection against desiccation of the seed on this side 
(figs. 100, 108). The walls of these cells become brown, but are not 
as greatly thickened as those of the integument itsself. 
It is clear that taken all together the structure of the carpel and 
seed coat of this Peperomia is much less highly specialized as a pro- 
tection against desiccation than that of these same structures in 
Peperomia pellucida. In fact all other species of Peperomia examined 
by the writer show greater thickening of these tissues than is seen in 
Peperomia hispidula. It therefore seems altogether probable that 
the present character of these structures in the latter species has 
arisen secondarily, and is related to the character of its habitat. 
The vascular system of the carpel, with its one slender bundle, 
is possibly to be regarded as secondarily derived from types like the 
Piptrs, with six longitudinal vascular bundles in the carpel (Johnson, 
1902, fig. 15). It must be recalled that the development of the ovary 
of Peperomia hispidula gives no hint that it has arisen by the coales- 
escence of three carpels, which does seem true of most species of 
Piper that have been studied . 
E. The Embryo Sac, Embryo And Endosperm 
I. The arches porium and tapetum. 
Of the group of hypodermal cells visible in the young ovule from 
the beginning, one axial cell becomes distinguishable, about the time 
the carpel is closing together, by its larger size and larger nucleus. 
This cell divides at about the time the integuments are initiated, to 
form a parietal or tapetal cell above and the definitive archesporial 
cell toward the chalaza (figs. 56, 57). In a few ovules two such arche- 
sporial cells were seen (figs. 113, 114), which as we shall see may 
often go on in their development and form two embryo sacs (fig. 120). 
No mitoses of the nucleus of the primary archesporial cell were seen, 
but from mitoses occurring just before and after this stage there can 
be no doubt that this mitosis is a normal vegetative one in which 
more than 20 chromosomes are concerned. 
