578 MR. W. C. WORSDELL ON THE DEVELOPMENT 
Development of the Ovule. 
At the earliest stage in the development, the young ovule 
appears as a papilla produced by local divisions in the cells of 
the outer layers of the placenta. Occasionally twin-ovules are 
seen developing together where ordinarily but one would occur. 
In the papilla the archesporium is first differentiated from a 
group of elements as an enlarging hypodermal cell with dense 
protoplasmic contents and a large conspicuous nucleus (Pl. XX. 
fig. 1,ar). Two such cells may sometimes develop for a time 
together; but finally one only persists, the other becoming 
crushed (figs. 8, 8). Limiting the archesporium on the outside is 
an are of smaller cells subsequently constituting a portion of the 
nucellus (figs. 1-3, 5, 7,8). Owing to division of the cells on 
the inner side of the archesporium, the ovule becomes pushed 
outward and increases in length and breadth, the cells of the 
protective arc on the outside at the same time dividing longitu- 
dinally. Very soon, as a result of the quicker growth of the 
cells on one side, the ovule bends over towards the opposite 
side, its apex being, at this period, directed parallel to the surface 
of the placenta (fig. 2). At this stage the walls of two or three 
of the outer cells on either side of the ovule, behind the apex, 
begin to bulge outward, this being the first indication of the 
differentiation of the integument. As the archesporium grows 
in length, divisions occur in the cells just mentioned, as also in 
some of those behind them, such that the nucellus and the 
integument become differentiated, the former remaining a single 
layer round the apex of the archesporium, but of more than 
one layer farther on the inside. The integument eventually 
becomes two layers thick. The apex of the ovule at length 
becomes directed perpendicularly to the surface of the placenta, 
assuming its mature anatropous position. 
In the further development of the archesporial cell no tapetal 
cells were seen to be cut off, such as occur in the majority of 
Dicotyledonous plants. 
This cell shortly afterwards becomes divided into two equi- 
valent cells by a transverse wall (figs. 4, 5). Each of these cells 
then divides again, so that a row of four cells is the result (fig. 6). 
Of these the hindermost, i. e. the cell farthest away from the 
apex of the ovule, alone increases in size, and gradually crushes 
and absorbs the three others (fig. 7). This is the young 
embry o-sac. 
