538 Brown: EMBRYO-SAC AND EMBRYO IN PHASEOLUS 
the innermost macrospore at the chalazal end develops into the 
embryo-sac, and I find the same thing true in Phaseolus vulgaris. 
In other Leguminosae, according to Guignard, two, three, or four 
macrospores may be formed and either the innermost spore or the 
one next it may develop into the embryo-sac. Saxton (1907) 
finds in Cassia tomentosa a deeply buried macrospore mother cell 
whose division forms a row of four macrospores, of which the 
one next to the innermost produces the embryo-sac. However, 
according to Martin (1914), in Medicago sativa, Vicia americana, 
and several species of Trifolium examined by him, an axial row 
of four macrospores is formed. 
The functional macrospore becomes several times as long as 
wide before its nucleus divides (PLATE 26, FIG. 11). The two 
. outer macrospores degenerate rapidly, and by the time that the 
developing macrospore reaches the binucleate stage they have 
usually disappeared entirely. 
After the first nuclear division in és functional macrospore, 
the two daughter nuclei pass to the respective ends of the sac 
(Fic. 12), and a large vacuole appears between them. After the 
second nuclear division each end of the developing macrospore 
contains a pair of nuclei (Fic. 13). The nuclei at the micropylar 
end usually remain close together, those at the chalazal end being 
further apart. After the third division, a een of four nuclei is 
seen at each end of the embryo-sac. 
The polar nuclei begin their migration very soon after the com- 
pletion of the last nuclear division. Cell division ensues, resulting 
in the formation of a typical seven-celled embryo-sac (FIG. 14). 
The egg apparatus presents the usual appearance; the polar nuclei 
lie a short distance away from the egg apparatus in the median line; 
at the stage shown in Fic. 14 they have not yet begun to fuse. 
The antipodal cells are typically triangular in section, and their 
nuclei are smaller than the other nuclei of the sac. A large vac- 
uole is characteristic of the embryo-sac at this stage, lying between 
the polar nuclei and the antipodal cells. This development seems — 
to agree, except in minor details, with that of other Leguminosae 
that have been investigated. Saxton (1907) found an absorptive 
tissue derived from the antipodal cells in Cassia tomentosa; 
Hofmeister (1858) failed to find antipodal cells in the members 
