256 Rickett.—Fertilization of Sphaerocarpos . 
division. It is also worthy of note that, in spite of the immense size of the 
female nucleus and the much smaller size of the male, the chromatic 
material which actually enters into the sporophytic nuclei is contributed 
approximately equally by each parent (except for the difference between 
4k 
the X- and Y-chromosomes), since a large part of the substance within the 
female nucleus passes into the cytoplasm after the nuclear membrane 
disappears. 
Summary. 
1. The antherozoid nucleus, after entering the egg, assumes the shape 
of a thick, curved rod surrounded by a clear space (Phase i). After about 
two hours it takes first an oval shape (Phase 2), then, about eight hours 
later, a spherical shape (Phase 3). Its body is in these stages dense and 
homogeneous. These changes occupy in all about twenty-two hours. 
2. The clear space surrounding the antherozoid nucleus becomes 
bounded by a membrane. The male nucleus now expands somewhat and 
its chromatic material assumes a more or less reticular structure, resembling 
that of the female nucleus at this time (Phase 4). In this condition the 
nuclei remain about twenty-four hours. 
3. The female nucleus then proceeds to the slow organization of 
chromosomes, while the male nucleus again contracts and loses its visible 
structure (Phase 5). In the egg cytoplasm, meanwhile, dense caps of 
homogeneous material appear opposite each pole of the female nucleus. 
These processes occupy on the average about twenty hours, the time being 
very variable. 
4. The polar caps in the egg cytoplasm enlarge until they completely 
surround the two nuclei, which now lie in contact. The male now organizes 
its chromosomes very rapidly, and the membranes of the two nuclei break 
down probably at the same time. Eight chromosomes can be counted 
in the male nucleus. A spindle cannot be distinguished in the cytoplasm 
on account of the dense mass of material there present. The first division 
proceeds very rapidly (Phase 6). About sixteen chromosomes can be 
counted. The first partition wall of the young embryo is transverse, as are 
the two succeeding ones in the majority of cases. 
5. Polyspermy occurs in about eight per cent, of the cases of fertilization 
observed. This, at least usually, results in the degeneration of the egg. 
In conclusion I wish to express my great indebtedness to Professor 
C. E. Allen, at whose suggestion and under whose supervision this work 
was done. 
Department of Botany, 
University of Wisconsin. 
