386 Cooke and Schively on Observations on the 



about, so that they He one above the other, just as does the 

 lower pair. The sac elongates steadily, and the connecting 

 thread of protoplasm between the two poles becomes con- 

 siderably longer. There seems to be no increase in the total 

 amount of cytoplasm present. 



Next, division occurs in these four cells. Similar pointed 

 spindles form, on which lie many small stout rod-like chro- 

 mosomes. The two spindles at the upper end show exactly 

 the same relation to each other as did the two spindles of the 

 preceding stage. Division of the two lower cells was not 

 observed, but it is supposed the spindles lie in the same rela- 

 tions as in the upper region, since the relative positions of 

 the nuclei after division indicate it. 



In the mature embryo sac, the cytoplasm is aggregated in 

 three distinct masses. It narrows toward the lower free 

 end of the ovule, and is broadest just below the micropylar 

 end. The eight typical nuclei are now present. The two 

 synergidal nuclei lie side by side just below the micropyle. 

 A little farther down is the tgg nucleus, larger and more 

 deeply stained than the synergids. Below is a sharp trans- 

 verse break in the cytoplasm. Right under this lie the two 

 fusion nuclei. They are seen to be approaching each other, 

 though lying some distance apart. Later they lie side by side 

 (Fig. 10), closely appressed and flattened against each other. 

 They are the largest, densest nuclei in the entire embryo sac. 

 They have a large amount of deeply stained chromatin, and 

 a very large, dense spherical nucleolus. At a considerably 

 later stage they are seen to have fused to form the single 

 large endosperm nucleus. 



Below, in the same mass of cytoplasm that contains the 

 endosperm nucleus, extends the long central vacuole before 

 noted ; it is surrounded by narrow protoplasmic walls. An- 

 other complete transverse split in the cytoplasm occurs 

 (Figs. 10, 11). In the lower cytoplasmic mass lie the three 

 antipodal cells, the lower two lying side by side, and having 

 the appearance of being separated by a faint cell wall. They 



