THE MORPHOLOGY AND AFFINITIES OF GNETUM 1 59 
I believe that the egg cytoplasm and membrane are always differen- 
tiated and it may be that in cases where they cannot be distinguished 
the egg nuclei have just been organized and that the cytoplasm and' 
membrane will be differentiated later. In any case the nuclei them- 
selves are always plainly differentiated. Usually two such eggs are 
present, often only one, and sometimes three. Figure 40 shows the 
upper end of a sac in which two eggs have been differentiated. The 
pollen tube is seen pressed against the sac. Figure 41 gives the 
appearance of the whole sac at this time. The eggs are also shown 
in the sacs in figures 42, 43 and 44. Figure 47 represents an egg 
nucleus alone. 
Apparently these eggs make their appearance only under the 
stimulus of the presence of the pollen tube against the sac. It seems 
that the pollen tube remains pressed against the sac for a long time 
before bursting in, because it is found in this position more commonly 
than in any other in ovules of about this age. One can frequently 
find sacs in contact with pollen tubes although no eggs have yet been 
differentiated. But before the pollen tube enters the sac, the eggs 
are always visible. Therefore one concludes that the eggs become 
differentiated only when the pollen tubes are in contact with the sac. 
The position of the nuclei which become transformed into eggs 
bears no definite relation to that of the pollen tube. Though they are 
aWays in the upper part of the sac they may be either directly under 
the pollen tube or at the opposite side of the sac and are often at some 
distance from the end. 
The fact that Gnetum forms definite eggs is one of the outstanding 
results of this investigation. It has always been supposed that any 
of the free nuclei in the gametophyte might be fertilized (Lotsy, 19). 
"It is in this stage that fertilization occurs, for the free nuclei are 
potential egg nuclei, although a group at the antipodal end of the 
sac may be as distinctly vegetative as are the antipodal cells of Angio- 
sperms" (Coulter and Chamberlain 8). If this is true then of course 
all the nuclei in an Angiosperm gametophyte are in the same sense 
potential egg nuclei. In fact the differentiation of special nuclei to 
serve as eggs makes the resemblance of the female gametophyte of 
Gnetum to that of Angiosperms still more striking. Particularly 
does it strengthen the resemblance, already frequently pointed out, 
to the irregular sacs such as those of Peperomia (Campbell, 6, Johnson, 
10, 11), Gunnera (Schnegg, 23), etc., in which many free nuclei are 
