106 FECUNDATION ; HETEROGAMETES, 
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 oosphere 
is then completed, and the end of the fertilization-tube remains firmly 
attached to it.” Although the presence of the male nucleus, while in 
the periphery of the egg, was not clearly demonstrated, yet this is not 
absolute proof to thecontrary. ‘+I have,” Trow continues, ‘* satisfied 
myself, however, of the presence of two nuclei in the egg at all times 
in this stage, one peripheral and one central, and the peripheral one 
always close to the point of attachment of the fertilization-tube.” 
sane 
-—— 
a, 
. : 
NW £g7 = 
= ‘Mu \ Ly as 
eg rom. \ oR 
J eas Br 
Re 
SS 
_ 
Fic. 38.—Young stages of two oégomia and two egg-cells of A. 
americana var, cambrica,—(After ‘l row.) 
A, section of young stage before delimination from hypha, 
showing cytoplasmic structure and nuclei. 
B, median section at stage preceding balling; 4 g. z., female 
gamete nuclei; deg. 2., degenerate nuclei. 
C, egg containing one nucleus; apex of conjugation-tube con- 
taining male nucleus has penetrated egg. 
D, egg from a 5-day culture, in which the two gamete nuclei 
are in contact ; m. g. ., male gamete nucleus. 
At a later stage obtained from a five-day culture the two nuclei are 
found applied to each other in the center of the egg (Fig. 38, D). 
They are in the resting condition, and about the same size, the male 
being distinguished from the female only by its smaller nucleolus. 
From the fact that the sexual nuclei were found side by side in a five- 
day culture, and from an examination of many hundreds of oospores 
from six- to eight-day cultures, it is inferred that about three days are 
required for the complete fusion, during which time the nuclei remain 
in the resting condition, a phenomenon of frequent occurrence among 
thallophytes. In the oospores of nine- or ten-day cultures, which 
have developed a well-differentiated cell-wall, only one nucleus was 
observed. Later, during germination, the fusion nucleus divides karyo- 
