158 
WALTER P. THOMPSON 
than the lower, the whole then taking on the form of an inverted 
flask. Usually the vacuole does not extend completely to the bottom 
of the sac, this end being occupied by a mass of protoplasm and nuclei 
(figs. 38, 39). This fact is important in connection with the formation 
of the endosperm. Figure 41 shows the appearance of the mature 
sac in G. gnemon and figure 39 that of G. sp. jj. Each is seen to be 
shaped like an inverted flask with a mass of protoplasm and nuclei 
at the lower end and a thin layer of protoplasm containing a single 
row of nuclei along the sides. Occasionally strands of protoplasm 
containing nuclei stretch across the upper end. In Gnetum gnemon 
the neck of the flask is not nearly so long as in G. sp. jj and other 
species. 
The nuclei have almost the same appearance throughout the 
development of the sac, but gradually get slightly larger. Each one 
contains very little chromatin matter and a large conspicuous nucleolus 
in the form of a hollow ball. The cavity at the center of the nucleo- 
lus is usually very plain. The divisions in the sac are simultaneous. 
The number of nuclei finally produced in G. gnemon is approximately 
256, which is the usual number found in Gymnosperms before wall 
formation takes place. It is evident therefore that in this species 
the development of the gametophyte follows the typical Gymnosperm 
method in all stages prior to the formation of cells. At this point 
the similarity ends. In G. sp. jj and G. moluccense the total number of 
nuclei is approximately double the usual Gymnospermic number or 
512. In other words another division of each nucleus has taken place. 
As stated by Thomson (30) the megaspore membrane (wall of the 
embryo-sac) is very thin. In all the species examined I could distin- 
guish only a single thin homogeneous membrane which almost disap- 
pears towards the top of the sac. In G. sp. jj this membrane becomes 
considerably thicker during the early stages of endosperm formation. 
After the pollen tube comes in contact with the embryo-sac a 
very important development takes place. One or more of the nuclei 
at the upper end of the sac become differentiated from the others and 
definitely recognizable as egg nuclei. They can easily be distin- 
guished from the remaining nuclei by their larger size, greater affinity 
for stains, very dense structure, and inconspicuous nucleolus. The 
other gametophytic nuclei always have a loose structure and very 
conspicuous nucleolus. It is not always possible to satisfy oneself 
that the egg nucleus has its own cytoplasm and limiting membrane. 
