27% Cook: DEVELOPMENT OF EMBRYO-SAC AND EMBRYO 
tapetal cells may be formed by a periclinal wall (/ 3) or by an 
anticlinal wall (f 4) or three may be formed by the formation 
first of an anticlinal wall followed by a periclinal wall in one cell 
only, or four may be formed by two periclinal walls followed by 
one anticlinal in one cell only, or by one anticlinal wall followed 
by two periclinal walls (/. 5). 
The formation of the potential and the functional megaspores 
was not observed but many cases of the growth of the functional 
megaspore and degeneration of the potential megaspores were ob- 
served (f. 6-9). In one case two well-developed functional mega- 
spores were observed lying side by side (/. 70). 
The embryo-sac is perfectly straight and develops rapidly, en- 
larging principally in the direction of its longer axis, the greater 
growth being towards the micropyle at the expense of the tapetal 
cells (f rz-r3). An abundance of starch usually appears in 
the developed megaspore and persists throughout the two- and 
four-celled stages (f 9, zz, 72). The antipodal cells are very 
small and disappear about the time of the conjugation of the polar 
nuclei (/ 73). In only one instance were they observed to per- 
sist until the beginning of the formation of the endosperm. 
With the formation of the endosperm nucleus the egg apparatus 
becomes very distinct (f 74, 75). The synergids are quite 
apparent and at least one of them persists for a very long time 
(f. 23, 28). 
Shortly after the conjugation of the polar nuclei (/ 73, 74 
75) and fertilization of the egg (/. 76) the endosperm nucleus 
divides and a very delicate but definite wall is formed across the 
sac (f. 16, 17) similar to that described by Schaffner for Sagit- 
taria (12). 
The upper nucleus thus formed moves toward the embryo and 
rapidly forms the endosperm (f 77 and fext fig. r). This end of 
the sac enlarges rapidly and becomes filled with endosperm (/. 
21) which persists until the embryo is fully formed but the cell 
walls gradually become thinner and the protoplasm gradually dis- 
appears as the embryo approaches maturity. 
The other cell formed by the division of the endosperm nucleus 
grows towards the chalazal end of the ovule, forming a tube by the — 
absorption of the nucellus and leaving in its trail a long string g 
