192 Johnson. — On the Nursing of the Embryo 
tip, which may consist of several rows of cells (Fig. 14). The 
freed nuclei divide, and that part of the embryo-sac which 
will be called the ‘placental embryo-sac tube’ comes to 
contain a long chain of nuclei imbedded in dense granular 
protoplasm, for most of its extent (Fig. 18). In the meantime 
changes have occurred in the nucellus-part of the embryo-sac. 
The three or four first endosperm-cells formed here are so 
large as to extend, each across the whole width of the sac 
(Fig. 15). Their nuclei then divide several times so that 
each primary endosperm-cell becomes multinucleate, round 
each secondary nucleus a cell-wall forms, and so the nucellus 
part of the embryo-sac becomes filled by isodiametric endo- 
sperm-cells. The embryo, for a long time unicellular, 
becomes pear-shaped, and in the condition of the endosperm 
just described consists of several cells (Fig. 15). It remains 
for a long time, as in many other parasites, undifferentiated ; 
there is no sign of a pro-embryo divisible into suspensor and 
terminal embryo-cell. The position of the embryo in the 
endosperm at this early stage is well worth noting, and one 
which is retained through all subsequent stages in the 
maturing seed (compare Figs. 15, 16). All degrees of the 
backward prolongation of the sac were found, from the earliest 
stage to its full course. Contrary, too, to what is generally 
supposed, all three ovules may be fertilised and the changes 
detailed above may occur, in part, in each one ; thus there is 
a possibility of the presence of three young seeds in one fruit 
(Fig. 13). The penetration of the placenta by three elongating 
embryo-sacs is very rare, by two is not unusual, by one only 
so general that for a long time I thought, from the prepara- 
tions made, it was the only case. I did not once find two 
prolonged embryo-sacs reaching to the base of the flower. 
Fig. 13 represents the usual place and stage at which the 
second embryo-sac ceases to develop. There can be little 
doubt as to the main function of the placental embryo-sac 
tube. The placenta is evascular, its cells are not provided 
with very rich contents, fusion between it and the adjacent 
vascular ovary wall does not take place ; the distance between 
