O’ NEAL: EMBRYO SAC DEVELOPMENT IN OENOTHERA 141 
until the embryo sac is matured. Fic. 18 shows the bi-nucleate 
stage of the embryo sac. This section is cut in such a way that 
the vacuole does not show, but a study of the adjoining sections 
reveals its presence. This stage of development follows shortly 
after that shown in Fic. 17, and the nuclei here shown divide 
almost immediately without changing position. This results in 
the tetra-nucleate condition shown in Fic. 19. Shortly after 
the formation of the four nuclei, plasma membranes appear 
around the cytoplasmic masses containing three of them and 
the usual egg apparatus with its two synergids and egg cell is 
formed, as shown in Fic. 20. The fourth nucleus usually draws 
away from the egg apparatus. While these changes have been 
taking place strands of cytoplasm have appeared in the vacuole, 
as is represented in the mature embryo sac given in the figure. 
Coulter and Chamberlain (3) listed Oenothera in the group 
of plants having ephemeral antipodals. The present writer at 
the outset, knowing what an easy thing it would be to overlook 
the fragments of these cells, had the feeling that this was likely 
the condition. Literally thousands of sections have been ex- 
amined for evidence supporting this view, but as stated above, 
the megaspore nucleus divides but twice, so the antipodals and 
one polar nucleus are completely lacking. This finding for 
Oe. rubrinervis is in keeping with that of Geerts (15) for Oe. 
Lamarckiana; Modilewski (26) and Ishikawa (17) for Oe. 
biennis; Reanek (24) for Oe. biennis, Oe. Lamarckiana, Oe. 
muricata, and various hybrids enichaied by crossing these 
species; and Werner (29) for Oe. Lamarckiana, Oe. biennis, 
Oe. rhizocarpa, Oe. tetraptera, and Oe. coccinea. 
The tetra-nucleate embryo sac-——The tetra-nucleate embryo 
sac has been reported for about sixty species of plants. Over 
half of these are from the order Myrtales, to which the Ona- 
graceae belong. The tendency to this condition seems rather 
wide spread in the Archichlamydae and is found in the Orchi- 
dales and Liliales of the monocotyledonous group. Doubtlessly, 
the development of the tetra-nucleate embryo sac is but one 
expression of the tendency to eliminate the divisions that occur 
after the reduction division of the mother cell. A few cases 
have been reported from the Primulales, a lower order of the 
Metachlamydae; but, as has been pointed out by Coulter (2), 
it is doubtful if this tendency is a very strong one in this group. 
