KING: CYTOLOGY OF ARAIOSPORA PULCHRA. 
233 
the point toward which they are both drawn. But this central 
ooplasm while highly differentiated, certainly appears, in many cases, 
almost homogeneous and, if this be true, the sexual nuclei as they 
approach its center, should, if not mutually attracted, assume a more 
nearly spherical form, a thing which they do not do. The fact that 
the anterior halves of the approaching nuclei are drawn out into 
sharp beaks suggests that the attracting force, if outside the nuclei 
themselves, is centered in a small area at their tips. 
The writer has seen no later stages of fertilization. From the 
time the sperm nucleus is introduced until the oospore has a thick 
wall and contains a conspicuous central globule, binucleate oospores 
may be found in practically all intervening stages (pi. 13, fig. 
20-22 ; pi. 14, fig. 25-31). A comparison of these figures (a por¬ 
tion of one nucleus in figure 25 (plate 14) appears in the next 
section) shows that the binucleate character persists during the 
formation of the central globule and the thickening of the oospore 
wall. It may also be seen that there are evidences of the presence 
of nuclear beaks in figures 25, 26, and possibly in 27 (plate 14). 
This would seem to indicate that fertilization had not taken place 
at this time. Figures 29, 30, and 31 (plate 14) represent sections 
through oospores that are practically mature. Even in figure 31 
an equally conspicuous nucleus shows in the next section. 
When does nuclear fusion take place? This point has been a 
puzzling one for it is extremely difficult to find uninucleate oospores. 
It is true that a few have been found in looking over a great num¬ 
ber of sections but even these few represented no particular stage 
in the development of the oospore, a.fact difficult to explain on the 
ground that they contain zygote nuclei. It may furthermore be 
stated that the writer has never seen a case where an empty antheri- 
dium was certainly connected with a uninucleate oospore. The most 
reasonable interpretation of the facts is that the two nuclei occurring 
in the developing oospores are the sexual nuclei and that nuclear 
fusion does not take place until later. This conclusion is supported 
by the following facts : — (1) The most mature oospores are only a 
couple of weeks old and, in all probability, are just starting on a 
long period of rest; fusion could occur somewhere in this period, 
possibly at its close. (2) No nuclear fusions or divisions were seen 
in the oospores. (3) There are invariably only two nuclei in the 
older oospores. (4) These two nuclei are always closely associated 
