636 Trow . — The Karyology of Saprolegnia. 
necessary for fertilization to take place in such cases. No 
one, for example, has been able to determine the presence of 
a permanent opening at the end of the pollen-tube of the 
Angiosperms., where fertilization undoubtedly takes place. 
This remark has a special significance if we remember that 
Hartog has actually described the passage of Monads into 
the hyphae of Saprolegnieae, and expressly states that the 
opening made is not a permanent one. It is well known too 
that in these plants little protoplasm escapes from the cut end 
of a hypha, the damage being repaired with extreme rapidity 
by the formation of a new piece of cell-wall, possibly owing 
to the presence of cellulose as a reserve material in a specially 
soluble form. 
The young wall of the oospore is generally easily seen 
owing to the slight contraction of the protoplasm induced by 
the method of preparation, as is represented in the binucleate 
oospore of Fig. 18. 
After a time, the two gameto-nuclei lie fairly closely together 
near the centre of the oospore. Fig. j 9 represents the young 
oospores in this condition. Nuclei are still to be seen in the 
antheridia and fertilization-tubes. The two nuclei do not 
always appear in the same section, so that careful drawings 
and comparisons have to be made to convince oneself that 
the oospore is always binucleate at this stage. The oospores 
of two large oogonia were investigated in this way, and a large 
number of other oospores examined in a less rigorous manner. 
As the result of these observations, extending to hundreds of 
oospores, I was forced to the conclusion that the young 
oospores are invariably binucleate. 
An examination of the nuclei in Fig. 19 shows the increase 
in size already described : the nuclei of the oospores are very 
much larger than the nuclei of the oospheres and fertilization- 
tubes. 
The study of 5 . Thureti was undertaken to place the 
process of fertilization beyond doubt. As already pointed 
out, the absolute identification of the species, owing to the 
behaviour of the cultures, has here become impossible. Figs. 20 
