Cytology of a new variety of A chly a americana. 159 
Fertilization. In sections passing through oogonia with 
unfertilized eggs, fertilization-tubes may be seen in all stages 
of development. They contain nuclei which correspond 
exactly with those of the oospheres, except that they are 
somewhat smaller. Large numbers of sections were examined 
to try and elucidate the mode of fertilization, but only one 
section, that reproduced in Fig. 45, appeared to be capable 
of throwing any light on the actual process. In this case 
it was possible to trace the fertilization-tube without a break 
into an egg which was already surrounded by a delicate 
membrane. The figure, combined with what we know from 
observations made on living material, suggests that the 
fertilization-tube grows up to the egg, presses against it, 
indents it, stimulates it to the formation of a delicate cell-wall, 
and grows obliquely into the mass of protoplasm, carrying 
at its apex a single nucleus. Later stages, such as that in 
Fig. 46, tend to show that the wall of the tube within the 
oosphere breaks down, the nucleus, together with a small 
quantity of protoplasm, is liberated, and so comes to lie in 
the peripheral part of the egg. The cell-wall of the oospore 
is then completed, and the end of the fertilization-tube 
remains attached firmly to it. It is not easy to see the 
male gameto-nucleus while still at the periphery of the egg, 
but the female gameto-nucleus in the middle is very obvious, 
for it appears to be just at this period that the nucleolus 
makes its first appearance in it as a small deeply stained 
spherical granule near its centre. I have satisfied myself, 
however, of the presence of two nuclei in the egg at all times 
in this stage, one peripheral and the other central, and the 
peripheral one always close to the point of attachment of 
a fertilization-tube. There can be no doubt whatever that 
whether the view taken here as to the actual mode of 
fertilization be correct or not, eggs at this stage contain 
two gameto-nuclei of diverse origin, the one male, and the 
other female. In Fig. 46, drawn from one of many oogonia 
observed in detail, section by section, the two lower oospores 
each contain two gameto-nuclei ; in the upper one, as shown, 
