74 WEATHERWAX: GAMETOGENESIS IN ZEA Mays 
large hypodermal cell near the tip of the nucellus (PLATE 6, 
FIG. 1). It soon divides periclinally, giving rise to a parietal cell, 
the tapetum, and a megaspore mother-cell; but no wall is formed, 
and the tapetal cell is immediately consumed (Fic. 2). The 
parietal layer of tissue, five to eight layers of cells in thickness, 
which is ultimately present (Fic. 16), is formed from epidermal 
cells by periclinal divisions (Fic. 2 and TExT-FIG. 1). 
In another connection (24, 
p- 492) the statement was 
made that, inasmuch as no 
evidence had been seen of the 





ALK disorganization of any of the 
fs MAL megaspores, all four probably 
ae e AY (} J, As, 7] sa S ; ’ p 
EY LAN Wiper “ functioned as in the lilies. 
NY But it has since been pointed 

out to me by Mr. E. G. 
a as Binucleate stage oF megaspore Anderson, of Cornell Univer- 
Tice uns cage a es ie ity, tat it eneh be the eae, 
ment; w, ovary wall; ”, tip of nucellus. the results of certain experi- 
ments on heredity in the en- 
dosperm must receive a new interpretation. Consequently, a 
thorough investigation of the development of the megaspore and 
embryo sac was thought profitable. 
The heterotypic division of the mother-cell is, in all essential 
details, similar to that in other plants (Fics. 3, 4). The chromo- 
somes are small and the karyokinetic figures indistinct; and the 
material is not satisfactory for giving any light on controverted 
questions of cytology in general. The bivalent character of the 
chromosomes at this stage is, however, beyond question. A wall 
is laid down between the two cells resulting from this division 
(Fic. 5). 
The more deeply-seated of these two cells next divides, giving 
rise to two megaspores (FIG. 6). The other cell begins to divide, 
but the process is arrested, usually at about the spindle stage, by 
the incipient disintegration of the dividing cell and the adjacent 
megaspore (Fic. 7). Thus, only the chalazal one of the four 
megaspore potentialities persists (FIG. 8). The absorption of the 
other three is not completed until the embryo sac is almost mature 
(Fics. 8-12). | 
