160 Trow . — Observations on the Biology and 
there is a male gameto-nucleus, but the female gameto-nucleus 
was in the next section. With two of the male gameto- 
nuclei fertilization-tubes are associated ; examination of the 
neighbourhood of the third in the adjacent section revealed 
the presence of one there also. The branching of the 
fertilization-tube is also seen. 
We are now able to fix a maximum limit for the time 
required in karyokinesis from the earliest stages up to the 
reconstitution of the nucleolus. The time cannot be greater 
than ten hours. 
Maturation of the oospores. Fusion of the gameto-nuclei . 
The male gameto-nucleus travels to the centre of the egg 
and places itself in contact with the female gameto-nucleus. 
Even from cultures five days old such preparations as that 
represented in Fig. 47 were obtained. The two nuclei are 
pressed closely together in one oospore, and they appear 
to have undergone partial fusion in the other. As a matter 
of fact they can only be recognized by their nucleoli. The 
male gameto-nucleus has the smaller nucleolus. At first 
I regarded this as distinct evidence of a very early fusion 
of the gameto-nuclei. Such preparations are uncommon, 
so that if this really represents a fusion it is probably a 
rapid one. 
The detailed examination of older oospores from cultures 
six, seven, and eight days old, and in which the determination 
of the relative ages of the oospores is not difficult, led to the 
discovery of the fact that oospores, one and two days older 
than those just described, always contained two gameto-nuclei^ 
while Those three days older seen in eight-day cultures some- 
times contained two and sometimes one. Fig. 48 represents 
oospores from an eight-day culture. At a glance, it is seen 
that the pairs of nuclei are in the resting condition, the central 
body is very large and the linin-threads are very evident. 
The nuclei in one oospore are approximated as if fusion were 
about to take place. Fig. 49 represents a zygote-nucleus 
in the act of formation ; the central body and nucleus are both 
elongated, but the fusion is nearly complete. Fig. 50 repre- 
