Reproduction of Cystopus Candidus , Ldv. 331 
in order to cover as much space as possible so as not to 
miss coming in contact with the nucleus of the oosphere 
(Fig. 14). In my preparations, the fertilizing tube was 
nearly always seen slightly contracted away from the proto- 
plasmic layer immediately outside and in front of it, leaving 
a space. This was probably due to the contraction con- 
sequent on the addition of re-agents (Figs. 11, 13, 15 and 16). 
Occasionally, however, this contraction had not taken place 
(Figs. 12 and 14). 
The fertilizing tube grows until it comes into contact with 
the central mass of dense protoplasm. This is shown in 
Figs. 15 and 16, two successive sections from the same 
oogonium ; one showing the nucleus of the oosphere, the 
other the male nucleus in the fertilizing tube. The fertilizing 
tube has contracted slightly away from the protoplasm in 
its immediate neighbourhood, but its original position with 
respect to the nucleus of the oosphere can be distinctly seen. 
Unfortunately this oogonium was cut very obliquely, so that 
the antheridium itself could not be seen ; nevertheless from 
examination of numerous sections at about this stage it is 
evident that the antheridium contains numerous nuclei. The 
apical part of the fertilizing tube is very thin and probably 
soft, and as soon as it has come into contact with the ovum- 
nucleus, the male nucleus is expelled and the tube im- 
mediately contracts, or rather collapses, and is withdrawn 
from the oosphere, leaving a large vacuole (a, Fig. 17) to 
mark its position. The two nuclei are left in close contact 
with one another (Fig. 17). The male nucleus is nearly 
always slightly smaller than the female. A delicate mem- 
brane, already indicated in Figs. 15 and 16, becomes now 
visible around the oosphere, separating it from the dense 
protoplasm. The two nuclei remain in contact for a short 
time and then fuse together (Fig. 20) to form the nucleus of 
the oospore. 
It may be well to refer here to previous observations on the 
fertilization of the Peronosporeae. De Bary points out (’ 84 ) 
that in Pythium , nearly the whole of the contents of the 
