1904] OPPERMAN: LIFE HISTORY OF ASTER 355 
little or no increase in breadth, but elongates rapidly, pushing 
down for a considerable distance into the nucellus, while the 
upper and central region of the embryo sac ceases to elongate, 
but grows to several times its original breadth. 
Considerable variation has been noted in the shape and size 
of the mature embryo sac, not only in the different species, but 
also in different ovules of the same species. These irregularities 
may be apparent at an early stage, as is shown in figs. 2 and 3. 
The embryo sac represented in fig. 3, although of the same 
Species as the one represented in fig. 2 and of a later stage of 
development, has grown much less in length. It is also apparent 
from a comparison of figs. 6 and 7 that, while the embryo sac of 
A. undulatus shows a remarkable growth in breadth near the 
micropylar end, the embryo sac of A. multifiorus, though slightly 
older than the former, has broadened very little in that region. 
The upper portion of the embryo sac of A. Novi-Belgit, like that 
of A. multifiorus, grows little in breadth, while the form of the 
embryo sac in A. Novae-Angliae (fig. 8) resembles very much 
that of A. undulatus. 
Soon after the embryo sac has reached the eight-nucleate 
Stage of development, three of the nuclei in the lower end of the 
embryo sac move downward to form the cells of the elongated 
antipodal region. The four nuclei in the micropylar end 
assume their characteristic arrangement and give rise to the egg 
apparatus and to the upper polar nucleus. The egg nucleus 
rests in the lower oval end of a pear-shaped cell, in a dense mass 
of cytoplasm. Above the nucleus the usual vacuole is found, 
which is very large in Aster, often occupying two-thirds of the 
entire oosphere. The synergids lie one on each side of both on 
the same side of the oosphere. Each may have the same rela- 
tive position with reference to the micropyle, or one synergid 
may extend farther into the micropyle than the other. They 
are usually densely filled with cytoplasm, but may be somewhat 
vacuolate. The nucleus of each synergid is much smaller than 
the egg nucleus or the upper polar nucleus, and may be placed 
Sentrally or at a point considerably above or below the middle 
of its cell, 
