Bliss. — A Contribution to the Life-history of Viola. 157 
Origin of Ovules. 
The ovary of the Violaceae is unilocular with three parietal placentae. 
At a very early stage the placental line is recognized by a layer of closely 
set cells differing from the other cells in their denser and more deeply 
staining cytoplasm. Very soon the placenta becomes more conspicuous by 
the rapid growth of the cells directly back of the placental region, so that 
the line of placentation extends out into the cavity of the ovary. It is 
interesting to note that before the primordial cells of the ovule are visible, 
the anther lobes are well developed, the cells of the tapetal and the sporo- 
genous tissue are clearly differentiated, and the spore-mother-cells are in the 
early prophase of the heterotypic division. The ovules arise as minute 
papillae on the placenta, and at first grow directly out into the cavity of the 
ovary. Soon, however, the ovule became a;natropous. 
Differentiation of Archesporium and Tapetum. 
The primary archesporial cell is hypodermal in origin, and is differen- 
tiated before the ovule has become anatropous. This cell differs from the 
cells of the surrounding tissue by its greater size, denser cytoplasm, and larger 
nucleus (PI. XVII, Fig. 1). A transverse division soon cuts off a tapetal 
cell from the primary archesporial cell (Fig. 2). The tapetal cell may divide 
first by an anticlinal or by a periclinal wall (Figs. 2, 3). Further divisions 
of the tapetal cells are variable, but finally a cap of considerable depth is 
formed, and the definitive archesporial cell comes to occupy a central 
position in the nucellus (Fig. 4). In Viola , the nucellar cap persists up to 
the time of embryo formation, and at the time of fertilization the pollen- 
tube makes its way through this tissue in its passage from the micropyle to 
the egg. 
The interesting phenomenon of twin nucelli was noted in several 
preparations. In one preparation observed, the embryo-sac was developed 
in each nucellus as far as the eight-nucleate stage, and the egg apparatus 
had been established. If in such cases fertilization should take place, we 
would have a case of polyembryony in Viola , or according to Ernst ( 4 ) 
a case of pseudo-polyembryony, brought about by the division of the 
nucellus at an early stage of development. 
Formation of the Axial Row. 
During the formation of the tapetal tissue the definitive archesporial 
cell increases in size, its cytoplasm becomes scanty, and the nucleolus 
appears as a densely staining granular mass of chromatin (Fig. 3). At this 
time the cells of the nucellus surrounding the archesporial cell are actively 
dividing. In the nuclear plate stage of the first division, the macrospore- 
