366 TRAXS ACTIONS AND PROCEEDINGS OF [Sess. lvi. 



ovum, below by the vacuole, and on its sides by the walls of 

 the embryo-sac. This fourth cell I propose to call, because 

 of its position and its nature, the micropylar primordial cell 

 (m. 2). c, figs. 25^ 25^ 26, 27, 28). 



In the basal half of the embryo-sac (fig. 24), we again 

 find two diasters, one occupying the very base of the sac 

 {ant.) and a second one {ant. + p.) placed obliquely to the 

 former. The diaster (ant.) gives rise to two antipodes, 

 which occupy the base of the sac (fig. 25) the line i-i in- 

 dicating their upper border, while the remaining diaster (ant. 

 -f p., fig. 24) gives rise to two nuclei, one of which surrounds 

 itself with protoplasm and a cell-wall, and becomes the 

 third antipode, while its sister-nucleus surrounded by naked 

 protoplasm is equivalent to a primordial cell, bounded above 

 by the vacuole, below by the antipodes, and laterally by the 

 embryo-sac-walls (a. p. c, figs. 25'\ 25^ 26, 27, 28). This 

 primordial cell occurring in the basal half of the embryo- 

 sac I shall call tlie antipodal one, to distinguish it from 

 the cell arising in the apex of the sac, namely the micropylar 

 primordial cell. 



To recapitulate shortly we find the embryo-sac to contain 

 in its micropylar end two synergida-, one ovum and a prim- 

 ordial cell ; in its basal end a primordial cell and three 

 antipodes, i.e., each end of the sac contains four cells, making 

 in all eiglit cells. 



What changes take place in the ovule during the maturation 

 of the embryo-sac will have to be studied next, as these changes 

 throw much light on facts which constantly occur in connec- 

 tion with tlie two groups of four cells enclosed by the sac. 



During the earlier stages of development the embryo-sac 

 increases in size mainly at its micropylar end, and hence the 

 periblem-cells of the ovule lying l)etween that end and the 

 dei-matogon are the first to suffer ; they degenerate and form, 

 along with the remains of the non-physiological sporocytes, 

 the cap round tlie apical one-third of the sac. When the 

 erabryo-sac is no longer able to increase in the micropylar 

 dir(!ction, it l)egins to bulge out laterally, enfeebles the 

 nucollar ])oriblGm-cells surrounding it, and ultimately kills 

 them. This latter change takes place in a very definite way, 

 as the degeneration spreads from the apex of the ovide down 

 to its base (fig. 27). That tin's should be so is explainable, for 



