364 Stephens . — • The Embryo-Sac and Embryo of 
were more satisfactory. Combinations of Licht-Griin with Diamant Fuchsin 
(a rapid and clear stain for embryological work), and of the haematoxylins 
with eosin were the chief stains used. 
Ovule and Embryo-sac. 
Throughout the order a four-carpellary, four-locular ovary is found. 
In Sarcocolla, Penaea , and Br achy siphon each loculus contains two to four 
erect anatropous ovules inserted in axile placentation near the base ; in 
Endonema and Glischrocolla the four ovules in each loculus are in- 
serted on an axile placenta, two erect and two hanging. Each ovule is 
surrounded in its earlier stages by two free integuments, each two cells 
thick (PI. XXV, Figs, i, 2) ; these, however, soon coalesce with one another, 
and with the nucellus, and are then recognizable, below the level of the 
micropyle, only as four regular cell layers at the periphery of the ovule 
(PI. XXVI, Fig. 24). In the later stages of their development the outer 
integument projects beyond the inner. Before they coalesce, the cells at 
the lip of each integument have begun to divide (Fig. 3), and their further 
divisions cause each lip to swell out into a cushion-like ring, which, meeting 
at the centre, blocks the micropyle (Fig. 24). 
The archesporium consists of a single sporogenous cell, which at its 
earliest recognizable stage is found sunk one layer deep beneath the 
epidermis (Fig. 1). The arrangement of the cell or cells in the layer 
immediately above it indicates that they and the sporogenous cell were 
probably derived from a single hypodermal cell by periclinal division. In 
one case only was there any sign of another sporogenous cell ; this is shown 
in Fig. 2, where the large cell above the embryo-sac is clearly differentiated 
from the rest of the nucellus by its size and staining properties, and may 
possibly represent a second potential megaspore mother-cell which has not 
functioned. The sporogenous cell of Fig. 1 enlarges considerably, becoming 
meanwhile sunk four to five layers deep by the periclinal divisions of the 
overlying cells, until it attains the size shown in Fig. 3, when it passes into 
the megaspore mother-cell condition ; the nucleus of the cell there figured 
is in an early stage of synapsis. In a preliminary note, 1 it was stated 
that this cell ‘appears to form a row of three (?) macrospores’. Further 
examination leaves no doubt that the reduction division takes place in the 
embryo-sac itself, and that a preparation formerly interpreted as a row of 
three megaspores, the upper two disintegrating, must really represent an 
enlarging mother-cell capped by crushed nucellar cells. Characteristic 
stages of the reduction division are shown in Figs. 4-8. These are 
apparently passed through with some rapidity, as ovules in the same ovary 
may show all stages from the mother-cell nucleus before synapsis to the 
four-nucleate sac of Figs. 9-1 1. Material was fixed at different times of day 
1 Stephens, 1908, p. 329. 
