334 Wager . — On the Structure and 
Guignard ( 5 91) the extremity of the pollen-tube swells up on 
coming into contact with the embryo-sac, and pushes its way 
towards the nucleus of the oosphere. As soon as it comes 
near the latter the male nucleus passes rapidly through 
the membrane and comes into contact with the nucleus of 
, the oosphere so quickly that it is rare to find it at any 
distance from the latter ; a state of affairs which is almost 
exactly paralleled by what takes place in Cystopus. 
In the Angiosperms the male nucleus, as it passes through 
the extremity of the swollen pollen-tube, is accompanied 
by a thin layer of protoplasm probably belonging to the 
generative cell. In Cystopus also the nucleus is accompanied 
by a small quantity of protoplasm at the time of fertiliza- 
tion, but whether or not any part of this passes with it 
into the oosphere could not be observed. In Angiosperms 
the male nucleus does not show any differentiated structure 
until it comes into contact with the female nucleus, when it 
swells up and assumes the normal structure of a resting 
nucleus. The two nuclei can be distinguished as separate 
structures up to the time of the formation of the chromatic 
segments. It is somewhat different in Cystopus ; the male 
nucleus as it passes into the oosphere is certainly smaller 
than the female nucleus, but it appears to show much the 
same structure. It increases in size, and then fuses with 
the female nucleus ; so far as I was able to observe the fusion 
is complete, and one nuclear membrane only can be seen at 
a stage much earlier than the appearance of the chromatic 
segments. These are however mere differences of detail, the 
important fact remains that the processes described are 
essentially similar in their chief features. 
Maturation of the Oospore. 
The fertilizing tube on its withdrawal from the oosphere is 
very much crumpled, as if by a sudden loss of turgidity due 
to the expulsion of its contents ; but it soon regains to some 
