

1917J WENIGER— EUPHORBIA 275 







The developing embryo sac becomes deeply imbedded in the 

 nucellar tissue. After some growth of the functional megaspore, 

 its nucleus divides (fig. 40) and one daughter nucleus moves to each 

 end of the cell. At this stage further growth takes place, and while 

 the first and second divisions of the nucleus (figs. 40, 41) are taking 

 place, a large central vacuole is formed which persists for some 

 time. An 8-nucleate stage was not found. In two cases 4 nuclei 

 were found at the micropylar end (fig. 42), but only 3 at the antip- 

 odal end of the sac. In most cases in which the egg apparatus 

 had been differentiated, no nuclei were to be found at the antip- 

 odal end of the embryo sac, indicating that the antipodal nuclei 

 (and cells, if formed) must be ephemeral, unlike the antipodal 

 cells of E. Preslii. Fig. 43 shows a sac with the egg apparatus 

 fully formed and the polar nuclei apparently about to fuse near 

 the egg, while the antipodal end of the sac shows 2 daughter nuclei 

 of a recent division, with a cell plate between them. It is possible 

 that after the second nuclear division in the developing megaspore. 

 one of the two nuclei at the antipodal end divides some time before 

 the other. One of the daughter nuclei of this (the third) division 

 might then move to the micropylar end and function as a polar 

 nucleus, its sister nucleus disintegrating before the remaining 

 nucleus in the antipodal end (a daughter nucleus of the second 

 division) finally divides. This explanation would also fit in with the 

 condition found in the sac shown in fig. 42, which had only 3 nuclei 

 at the antipodal end. 



Fig. 44 shows another peculiar embryo sac in which there are 

 plainly 8 nuclei at the antipodal end of the sac, at least 3 of which 

 are surrounded by cell membranes. In this case, it is conceivable 

 that each of the 4 nuclei at the antipodal end of the sac has divided 

 and that none has as yet disintegrated. In all but these cases, the 

 antipodal nuclei (or antipodal cells) had disintegrated. The egg 

 apparatus seems to be quite typical (figs. 43, 45). At first the nu- 

 cleus of the egg occupies the center of the cell, but later, as the egg 

 grows, the nucleus moves to the side of the cell farthest from the 

 micropyle. The egg is spherical, and its nucleus is not, in general, 

 larger then the nuclei of the synergids. In the sac shown in fig. 45 

 one of the polar nuclei lies close to the egg, while the other seems 



