1908] BROWN—PEPEROMIA 457 
first four nuclei in the embryo sac of any plant in which a row of 
megaspores is not formed are megaspore nuclei, but simply as sug- 
gesting that in most cases we have no adequate proof of this, and that 
in the present state of our knowledge there is at least one other way 
in which some of them may be regarded. 
The homologies in all these cases may be cleared up by further 
work. We have, however, no right to push them further than the 
present evidence justifies, or to suppose that all plants must behave 
alike in this respect, when we consider the large number of different 
analogous organs which have been arrived at by very diverse methods. 
Summary 
The archesporium of the species of Peperomia studied arises as a 
single hypodermal cell, which cuts off a single parietal cell and then 
forms the embryo sac directly. 
The first division of the embryo sac nucleus is heterotypic. The 
nucleus goes into synapsis. This stage is followed by an apparently 
continuous spirem. This splits longitudinally but later the two 
halves come together again. The chromosomes are formed from 
loops in the spirem. When these divide, they seem to separate two 
parts of the spirem which were originally placed end to end. 
The second division may divide the chromosomes along the 
longitudinal split seen in the prophase of the first division. 
In the third division of the embryo sac nucleus of P. Sintensii, no 
cell plates were seen on the spindles, but in the last division cell walls 
are formed on all the spindles. These walls cut off, against the 
embryo sac walls, one of each of the eight pairs of nuclei, and leave 
the other eight free in the cytoplasm. These free nuclei fuse to form 
the endosperm nucleus. The egg and a nucleus with the position of 
a synergid are cousins. The other six nuclei which are cut off against 
the embryo sac wall finally degenerate. 
The mature sac contains sixteen-nuclei, which are apparently 
derived from four megaspores. That the first four nuclei of the 
embryo sac are megaspore nuclei is indicated by the fact that the first 
division of the embryo sac mother cell nucleus is heterotypic and 
reducing, and that in P. pellucida cell plates are formed on the 
Spindles of the first two divisions, while in P. Sintensii. and P. 
