32 Gibbs. — Notes on the Development and Structure of 
The embryo- sac after elongating at the expense of the primary axile 
row of cells (Figs. 5, 6, 7, e . s.), expands by the absorption of the limiting 
concentric nucellar layer, which in this stage shows starch contents (Figs. 6 
and 7, per. l.st.). Progressive digestion of these limiting layers is shown by 
the existence, in contact with the embryo-sac, of disorganized cells, which 
remain in the position of, and can be traced back to, the layer of which 
they formed part (PI. V, Figs. 6 and 7, dis. c.). 
At this stage the embryo-sac contains eight free nuclei, and these 
quickly differentiate into the two synergidae and oosphere, three antipodals 
and two polar nuclei (Fig. 6 , syn. 00s. ant. p. n.). The cells of the nucellus 
in the immediate vicinity of the antipodals present the same unattached 
and partially digested appearance as those surrounding the rest of the 
embryo-sac (Figs. 7 and 8, ant.). No evidence points to the antipodals 
influencing the solution of tissue in contact with them. They are ephemeral, 
disappearing after fertilization ; and even before their differentiation the 
disintegrating changes in the nucellus are apparent. This seems to show 
that the actual cytoplasm of the embryo-sac is the active digestive agent 
up to fertilization, and also to a certain extent afterwards. 
The synergidae are well defined. They are long cells, and contain 
large nuclei (Fig. 7, syn.). 
Fusion of polar nuclei. The fusion of the two polar nuclei into one 
definitive endosperm-nucleus occurs some time before fertilization (Fig. 7, 
d. n.). The definitive nucleus resulting from the fusion is very large, with 
a well-marked nucleolus and dense reticulum. It occupies the centre of the 
embryo- sac towards the upper portion, and is in contact with the oosphere. 
The latter, which lies against the synergidae and near the embryo-sac wall, 
is smaller with a more alveolate reticulum (Fig. 7, 00s.). 
The fact that the nuclear membranes of the definitive nucleus and 
oosphere are in contact is characteristic of Stellaria media (Fig. 9, d. n.). 
In other species examined, this was never found to be the case, some 
cytoplasm always intervening (PL V, Fig. 8, d. n.). At this stage a very 
long rest occurs. It is on that account the most easy to obtain, and was 
found to occur in sections both of the expanding bud and open flower. 
Progressive development of endosperm , perisperm , and embryo after 
fertilization. The pollen-grains settle on the papillae of the stigma, as was 
correctly figured by Unger ( 4 ), the tubes growing along the cell-walls, but 
not penetrating them as he describes. They continue to force their way 
between the cell layers composing the tissue of the style which is in direct 
continuity with that of the septa of the ovary. 
These septa consist of loose, spongy tissue which forms papillae on 
each surface, and it is on these papillae that the micropyles of the ovules 
abut. This fact explains the definite orientation of the two rows of ovules 
in each loculus. 
