and Fertilization in Oenothera. 
281 
An axial row of four megaspores is formed by two successive divisions 
of the embryo sac mother-cell. Text-fig. I, 1, illustrates the early 
anaphase of the homotype division, in each nuclear plate of which seven 
chromosomes are clearly visible. Having finished the tetrad division, the 
nuclei of the micropylar and chalazal megaspores soon enter into a resting 
condition, while those of two intervening ones still remain in telophase 
surrounded by a thin layer of protoplasm (Text-fig. I, 2). Text-fig. I, 3, 
shows a little advanced stage, the uppermost and lowermost ones being 
enlarged by vacuolization, and the two intervening ones at the same time 
disintegrating. Then one of the survivors, whether micropylar or chalazal, 
becomes functional (Text-fig. I, 4, 5). According to Geerts ( 21 ), in 
Oe, Lamarckiana the uppermost megaspore is functional; the same was 
also reported by Modilewski ( 42 ) for Oe. biennis, while Davis ( 15 ) stated 
that in Oe. biennis often the uppermost, but sometimes the lowermost one 
develops. On the other hand, Werner ( 73 ), who studied Oe. biennis , 
Oe. Lamarckiana , and several other species of Oenothera , obtained the 
same result as reported by Geerts and Modilewski. In the species used 
for the present investigation those phenomena just mentioned above equally 
happen ; the fact can quite easily be seen if sufficient number of preparations 
are examined. Both the uppermost and lowermost ones often simul¬ 
taneously develop, as will be fully described farther on. 
The primary embryo sac cell enlarges and the nucleus passes to the 
upper pole, the lower part being nearly occupied by an enlarging vacuole 
(Text-fig. I, 5). The nucleus divides twice (Text-fig. I, 6, 7, 8, 9); the 
spindles of the last division are, if the available space permits, as observed 
in many cases, perpendicular to each other (Text-figs. I, 8, and III, 10). 
The daughter nuclei derived from the upper nucleus are destined to 
become those of the synergids, while those from the lower nucleus become 
the egg and pole nuclei. Text-fig. I, 10, represents a section of a young 
embryo sac, in which the arrangement of two sets of the nuclei are clearly 
shown. The tetranucleate embryo sac is attained in such a way. 
Text-fig. I,- 11, shows a mature typical embryo sac of Oenothera , in 
which the egg-cell (e.c.) is situated between and just back of the synergids 
(syn.), and only the lower part of the former peeps through the space 
between the free ends of the synergids. The upper free surface of each of 
the synergids is horizontally notched by an indentation and presents a visor¬ 
like appearance (Text-fig. I, 11, 12, ind.). Neither Modilewski, nor Geerts, 
nor Werner mentions or figures the indentation of the synergids in Oenothera , 
but Renner’s illustrations somewhat suggest its presence. The indentation 
of this kind has been either reported or delineated for several other plants 
since Strasburger’s description for Santalum albnm (66); for instance, in 
Helianthns animus by Nawaschin ( 46 ), in Parnassia palustris , Saxifraga 
ligidata , S. Sponheimica , N. cordifolia , Heiichera broxioides , and Drosera 
