250 Rickett.—Fertilization of Sphaerocarpos. 
ing. This, however, must have been rare, if it occurs at all, again for the 
reason that only cases of Phase 1 are found within the two hours following 
flooding. We may therefore, I think, conclude that the variation in the 
times at which stages are found is due to variations in the rate of the 
process rather than in the time of its starting. 
Doubtful Cases. 
In a number of the cases listed in Table I, the male nucleus was not to 
be seen. The female nucleus and cytoplasm, however, showed all the 
changes characteristic of the fertilization process, at one phase or another. 
Since no eggs are found in this condition in material which has not been 
flooded or afforded other opportunity for fertilization, these are thought to 
be true cases of fertilization in which the male nucleus was accidentally lost 
in making the preparation. In one case the male nucleus was found 
apparently inside the female nucleus. Closer examination revealed the fact 
that it was at a higher focal level than anything else in the egg ; and that 
in the next section there was a clear space surrounded by a distinct mem¬ 
brane, the latter in contact with the membrane of the female nucleus. 
Evidently the knife had caught the chromatin of the male nucleus without 
cutting it, dragged it out of its proper place, and left it in a section in which 
it did not belong. Something of this sort may have happened in some of 
the doubtful cases referred to. 
Here arises the question whether parthenogenesis occurs. The number 
of doubtful cases referred to above amounts to about 6 per cent, of the total 
(19 out of 307 cases). If this proportion of all the sporophytes formed 
resulted from parthenogenesis, we should expect to find a fair number of 
sporophytes in purely female cultures. As a matter of fact, the reverse is 
true. In the great majority of female cultures no sporophytes are found ; 
and in cases where they do occur, their origin is always traceable to a male 
plant that has somehow found its way into the pot, or to an accidental 
flooding of several cultures (including males) at the same time, or to some 
similar accident. It might be supposed that the act of flooding the plants 
may in some way furnish a stimulus by which a few eggs are enabled to 
develop parthenogenetically. This, however, seems rather far-fetched ; 
especially as female cultures have often been flooded by accident, without 
the resultant appearance of any sporophytes. 
There seems, therefore, little doubt that the development of an egg 
into an embryo is in all instances the result of a sexual process—that is, 
that parthenogenesis never occurs, and that cases that might seem to 
suggest it are due only to accidents of technique. 
Polyspermy. 
In something over 8 per cent, of the cases of fertilization observed, more 
than one male nucleus was present in the egg cytoplasm. These cases are 
