230 FISHER: SEED DEVELOPMENT IN PEPEROMIA 
archesporial cell without cutting off a parietal or tapetal cell. 
In Burmannia Championii this forms sometimes three, but 
usually four megaspores, and a typical eight-nucleate embryo 
sac develops from one of these, while the remaining two or three 
degenerate. In B. candida the definitive archesporial cell divides 
into two cells, the chalazal one giving rise to a typical eight-nucleate 
embryo sac, while the other degenerates. The division of the 
definitive archesporial cell is the heterotypic reduction division; 
therefore, the cell which gives rise to the embryo sac is the mor- 
phological equivalent of two megaspores. In B. coelestis, as a 
rule, the definitive archesporial cell develops directly into the 
embryo sac, without cutting off any non-functional megaspores. 
A typical eight-nucleate embryo sac is developed here from the 
morphological equivalent of four megaspores. It is interesting to 
note here that the end product in all three cases is a typical eight- 
nucleate sac, whether it is developed from one megaspore or from 
the morphological equivalent of two or of four megaspores. 
In the genus Euphorbia, two species, E. procera and E. palus- 
tris, both investigated by Modilewski (49, 51, 52), have sixteen- 
nucleate embryo sacs, while at least thirteen other species of the 
same genus, investigated by the same author, have typical eight- 
nucleate embryo sacs. The latter condition was also found in 
Ricinus, Phyllanthus, Securinega, and Croton, four related genera 
belonging to the same family, the Euphorbiaceae. 
Within a single species there is sometimes striking variation, 
as in Epipactis pubescens (Brown & Sharp, 5), where usually the 
embryo sac arises from the innermost one of three megaspores, 
but in other cases four megaspores take part in the formation of 
the sac. The authors further state that there is some evidence 
that the embryo sac may at times be derived from two megaspores. 
In Salix glaucophylla (Chamberlain, 11) there is even greater 
variation than in Epipactis pubescens. 
That the origin of the embryo sac from the morphological 
equivalents of four megaspores as found in Peperomia is a derived 
condition rather than primitive, is further indicated by the fol- 
lowing considerations: 
(1) The vast majority of the embryo sacs of Angiosperms 
arise from a single megaspore, and the exceptions are not limited 
