FISHER: SEED DEVELOPMENT IN PEPEROMIA 225 
species of Peperomia, namely: P. reflexa, P. verticillata, P. scandens, 
P. Fraseri var. resediflora, P. blanda, P. galioides, and P. Langs- 
dorffit(?). Similar evanescent separating walls occur in Smilacina 
stellata (McAllister, 45) and in Epipactis (Brown & Sharp, 5), 
in which cases it is plain that they are megaspore walls. Wiegand 
(79) reports an evanescent wall between the first two nuclei in 
the embryo sac of Convallaria, in which case there are no degener- 
ating megaspores, but the definitive archesporial cell forms the 
embryo sac directly, and this wall very probably represents a 
megaspore wall. In this case, however, only the heterotypic 
division is followed by an evanescent wall. 
The appearance of separating walls is, however, not absolutely 
essential in the formation of megaspores in cases where it is 
generally admitted that megaspores occur, e. g. the walls usually 
do not appear in Crucianella (Lloyd, 41), or in Asperula (Lloyd, 
41), and sometimes not in Eichhornia (Smith, 68) or Avena 
(Cannon, 10). In each of these cases, however, the embryo sac 
develops from a single megaspore nucleus, while the others de- 
generate, regardless of the absence of walls. But, since separating 
walls do generally appear between the megaspore nuclei in other 
plants, their presence in Peperomia certainly strongly favors the 
homology. 
Another explanation of the occurrence of these walls, in har- 
mony with Campbell’s (7) view, was suggested by Brown (4) and 
immediately rejected. He says: ‘If the walls corresponded to 
those of prothallial cells, we should expect to find them in the 
third division, but here not even a cell-plate was seen. Besides 
this, the nearest phylogenetic relatives in which the first divisions 
of a megaspore result in a cellular structure are found among the 
leptosporangiate Filicales, where the heterospory is supposed to be 
of rather late origin, and it does not seem probable that Peperomia 
has reverted to the characters of an ancestor as remote as one in 
Which we would find the first divisions of the megaspore giving 
rise to a cellular structure.” 
Since the separating walls occur in Peperomia following the 
first and second divisions only, in the embryo sac, and not after 
the third division, it is difficult if not impossible to conceive of 
any satisfactory homology for them, except that with the mega- 
