Campbell .• — The Embryo-Sac of Peperomia . 105 
division, and gives rise to several (3-4) layers of cells between 
the apex of the embryo-sac and the epidermal layer of the 
nucellus (Fig. 1, t). 
The inner archesporial cell becomes at once the mother- 
cell of the embryo-sac. 
The Embryo-Sac. 
The most remarkable fact brought out in the study of 
the development of the embryo-sac was the behaviour of the 
nuclei, which differ remarkably from those of other Angio- 
sperms. The marked polarity of the typical embryo-sac was 
found to be entirely wanting, and the nuclei were uniformly 
distributed. Most important of all was the further division, 
unique so far as is at present known among Angiosperms, of 
each of the eight nuclei, so that there are normally sixteen 
nuclei in the unfertilized embryo-sac (PI. VI, Fig. 1). 
The sixteen nuclei are at first entirely similar, and equally 
distributed in the rather thick cytoplasmic layer which sur- 
rounds the large central vacuole. As the embryo-sac develops, 
a certain number of the nuclei, usually but not always eight, 
approach, and about them there is an accumulation of cyto- 
plasm (Figs. 2, 3, E. n). This group of nuclei is often placed 
at the chalazal end of the embryo-sac, and much resembles 
a group of antipodal cells, although, as we shall see, they are 
not the homologues of the antipodals of the typical Angio- 
sperm embryo-sac. 
At the micropylar end there may be found two or three, or 
occasionally more, nuclei, while the remainder are arranged 
without definite order about the wall of the embryo-sac. Of 
the nuclei at the upper end of the sac, one soon becomes 
somewhat larger than the others, and there is an accumulation 
of cytoplasm about it, which is bounded by a more or less 
evident protoplasmic membrane (Figs. 3,4, 0 ) ; but this is not 
so evident, nor is the egg-cell thus formed so large, as 
Johnson describes for his preparations. This, together with 
some other slight variations, suggested that perhaps his plant 
