the morphology and affinities of gnetum l6l 
9. Fertilization 
The entrance of the pollen tube into the embryo-sac will be de- 
scribed under the head of fertilization, although in some species at 
least several important events intervene between the entrance of the 
tube and the essential act of fertilization, the fusion of male and 
female nuclei. 
The point of contact between pollen tube and embryo-sac varies 
in position but it is usually at the side of the expanded part of the sac. 
The tube nucleus takes up a position at the side of or behind the male 
cells. The contents of the pollen tube are discharged into the sac in 
the usual way. Both male cells, the tube nucleus, and a certain 
amount of cytoplasm pass in. The contents of the sac draw back 
slightly though not pushed back by any wall or mass of protoplasm. 
The male cells then make their way to one of the eggs, often traversing 
a considerable space in doing so, and leaving the tube nucleus behind. 
Figure 41 shows the general arrangement of the sac and tubes. One 
tube is entering at the left and another further up at the right. The 
egg is visible at the inner edge of a mass of cytoplasm. Figure 42 
shows part of a sac under greater magnification. The male cells 
and tube nucleus are just entering and the two eggs are to be seen 
further down in the sac. Figure 43, introduced for another purpose, 
represents about the same stage. In the case represented in figure 
44 the male cells have penetrated far into the sac towards the egg. 
The clear space ahead bounded by a partly collapsed membrane is 
typical. The subsequent events depend upon the species. 
In G. sp. jj a considerable time elapses before the actual fusion 
of the nuclei, and in the meantime important events take place in 
endosperm formation. The egg and male nuclei are then found in a 
definite chamber partly or wholly surrounded by cells of the endosperm 
formed in a way to be described later (page 34). Figure 45 shows a 
large cell containing the egg nucleus and the two male nuclei, the 
whole cell surrounded by the cells of the endosperm. Further away 
are free nuclei. In figure 49 the cells are seen to have formed around 
the end of the pollen tube which contains the tube nucleus. A large 
cell in the center contains the egg and male nucleus. Down in the 
neck of the flask are the endosperm cells which extend right to the 
bottom of the flask. Figure 50 shows the two distinct male cells in 
contact with the egg, all three enclosed in a definite chamber. 
