Tree (Ginkgo biloba, L.). 123 
of the embryo-sac, which appears as a column supporting at 
its apex the nucellar protuberance. 
It is noteworthy that the cells surrounding the ovum are 
characterized by thick and deeply stained walls, and contain 
abundant contents and large nuclei; the walls of these cells 
are penetrated by well-defined pits, as in some Cycads 1 and 
Conifers. The drawing shown in Fig. 48, PI. IX, illustrates 
the appearance presented in an apical view of the endosperm 
taken from a seed which had fallen from the tree; two arche- 
gonia are seen in an oval depression, one on each side of the 
vertical outgrowth of the embryo-sac. Before fertilization 2 
the nucleus of the egg-cell takes up a position just below the 
neck-cells, and a canal-cell is cut off early in September; the 
nucleus then moves towards the ovum and fertilization occurs. 
Fertilization is followed by a division of the oospore nucleus 
into two; each daughter-nucleus divides repeatedly, and 
eventually cell-membranes are laid down. The formation of 
the cell-walls is succeeded by division of the cells, growth being 
particularly vigorous in the lower part of the oospore, which 
constitutes the vegetative part of the embryo and gradually 
becomes differentiated, early in October, into the two cotyle¬ 
dons 3 . It has often been stated that fertilization does not take 
place until the ripe ovules have fallen from the tree ; this point 
has recently been investigated by Hirase 4 , who finds that some 
seeds at least contain a more or less developed embryo while 
still attached to the parent plant. 
The ripe ovule of Ginkgo is enclosed by a thick fleshy 
integument, succeeded internally by a woody envelope ; the 
upper part of the endosperm, d , after the removal of the hard 
shell (Fig. 45, b , PI. IX), is covered by a thin papery membrane, 
c, which represents the crushed remains of the nucellus. There 
is a close resemblance between the seed shown in Fig. 45 
and a seed of a Cycad ; in each the crushed nucellar tissue is 
represented by a thin membrane between the woody portion 
1 Treub. (’84) ; Ikeno (’98). 2 Hirase (’95), (’98). 
3 Strasburger (’72), p. 312 . 
4 Hirase (’94). We are indebted to Dr. Donald MacAlister for a translation 
from Japanese of Hirase’s paper. 
