Development of the Ovule, Embryo Sac and Embryo of Hydnora africana. 29 
recognisable, but a hypodermal cell larger than the rest becomes at once the 
megaspore mother-cell (Fig. 2). At this stage a curious thickening is seen 
at the top of the megaspore mother-cell and persists till a later stage. 
The megaspore mother-cell functions as an embryo sac directly, without 
first dividing into four megaspores. The nucleus divides into two by the 
heterotypic division (Figs. 3 and 4). The sporophyte number of chromo- 
somes is believed to be twenty-four,* and in the reduction division twelve 
were counted. Vacuoles appear in the embryo sac after the first division 
and the two nuclei arrange themselves at the poles (Fig. 6). The stages 
showing the homotypic division of the two nuclei into four were also seen 
(Fig. 7). Fig. 8 shows the embryo sac with an egg cell nucleus, two 
synergids, two fusing polars, three antipodals and a pollen tube, with the 
pollen tube nucleus and two curved male nuclei. Stages were seen in the 
progress of the polar nuclei towards the centre of the sac, and they fuse 
before fertilisation (Fig. 8). The antipodals may also disintegrate and 
disappear before fertilisation. Cases believed to show actual fertilisation 
were observed, but they have not been figured as the evidence was inconclusive. 
The embryo divides into two cells by a transverse wall and transverse 
divisions continue till a very long chain of cells is formed. As many as 
fifteen cells were counted in a chain in one proem bryo. Then longitudinal 
divisions occur in about the fifth, sixth, seventh, eighth and ninth cells 
from the distal end and these cells alone give rise to the embryo proper. 
The longitudinal divisions begin even before the divisions in the distal part 
of the filament are complete. The cells of the suspensor slowly shrink and 
at least the proximal cells disappear gradually, while the distal cells persist 
in the most mature embryo observed. Fig. 12 shows two longitudinal rows 
of four and three cells each and Fig. 13 shows two longitudinal rows of five 
cells each. 
Discussion. 
The massive integument seems to be an unusual feature in this species, 
as generally two integuments prevail among Archychlamydeae, except in 
some species of Eanunculus and Leguminosae (4). 
Among Archychlamydeae nearly all the species investigated have three 
or four megaspores (except in three genera of Piperaceae), and a row of four 
megaspores seems to be less common than a row of three (4). In this plant 
the megaspore mother-cell does not divide at all but directly functions as 
the embryo sac. 
The curious thickening which is seen at the top of the megaspore mother- 
cell, and which persists till a later stage, was thought at first to be the remains 
of a parietal cell cut off from the archesporial cell, and a careful examina- 
* Twenty-three were actually counted, but it is presumed that twenty-four were 
present. 
