Some Problems of Reproduction: a Comparative Study of ...

SOME PROBLEMS OF REPRODUCTION. 37
nucleus occur as follows:—The first differentiates an Apical
(N a a) and a Basal nucleus (N a b) respectively. Each of these
again divides to form a pair of nuclei nearly superposed, which
we term and letter Apical (N s a), Subapical (N 2 sa), Subbasal
(N 2 sb), and Basal (N 3 b) respectively. Each of these four
again divides to form a pair of nuclei of the degree N s . The
Apical pair (N 3 a + N 3 a) and Basal pair (N 3 b + N s b) are collateral;
the Subapical and Subbasal pairs are superposed to
form a file of four nuclei, which we name and letter Upper
and Lower Subapical (N s usa + N 3 lsa), and Upper and Lower
Subbasal (N 3 usb + N 3 lsb) respectively. Of the cytoplasm
lining the cell-wall and surrounding the immense central
vacuole, each nucleus attracts a certain portion so as to form
a naked "free cell" somewhat ill-defined, and indeed anything
but free. The following schema (Fig. 4) shows the for-
rN>a-
-N 2 b-
Synergids
N 3 a N 3 a Egg apparatus.
(
Oospbere i
N 3 usa j
I
lN 3 lsa
ilsb
N 3 b N»b I
Endosperm
nucleus.
! Antipodal
! cells.
FIG. 4.—Schema of divisions in embryo-sac; the vertical lines separate