140 TRANSACTIONS AND PROCEEDINGS OF THE [Sess. lv. 



examination. As tlie primary wall formed across the arche- 

 sporium is thicker than the secondary walls, it is only natural 

 that the thicker one should be the more conspicuous when both 

 undergo the mucilaginous change. This gelatinous appear- 

 ance of the cells is in every respect identical with that 

 taking place in the walls of sporocytes of other sporangia ; 

 and as it takes place before any sign of disorganisation 

 of the vsister-cells of the embryo-sac is visible, and as it 

 takes place in the walls of the embryo-sac, Strassburger's 

 and Ward's interpretation as to the mucilaginous change 

 being the initial steps towards a breaking down of the sister- 

 cells of the embryo-sac is not correct. 



The lowest cell in the row developes into the embryo-sac 

 thus : it increases considerably in size, not at first at the 

 expense of its sister-cells, i.e., it does not react on the other 

 cells by pressure, but seemingly grows to a larger size, as it 

 has become parasitic on the plerome-elements, for its wall in 

 direct connection with the latter does not show the mucil- 

 aginous appearance like the remaining sides. At this time 

 a vacuole is formed in the apical half of the young embryo- 

 sac close to the nucleus, and now growth of the sac takes 

 place rapidly, specially towards the apex of the ovule, the 

 sister-cells of the embryo-sac are compressed and show 

 signs of degeneration. The growth of the embryo-sac is so 

 rapid after the vacuole has appeared, that the latter seems 

 to me to be of the highest physiological im2>ortance in helping 

 to dilate the growing cell. 



A similar vacuole lias been observed by Stassburger in 

 Senecio vulgaris below tlie primary nucleus. It is evident, 

 therefore, that this vacuole appearing before the division of 

 the primary nucleus cannot represent a diHluent cell- wall; 

 but its large size is rather the cause of the non-formation of 

 a cell-wall dividing the embryo-sac into two cells. That 

 occasionally, though rarely, a cell-wall is formed after the 

 division of the primary nucleus is evident from Strass- 

 burger's* description and drawings of the young embryo-sac 

 of Orchis i)cdlens. 8e})ta running across the embryo-sac are 

 )igur-ed by the same author for Antliericum, Allium, &c., 

 Ward has found and figured a dilHuent partition in Lobelia, 

 >iyp]iilHica, and in Myosurus a very transient wall of the 

 vacuole iippears across the anterior third of the vacuole. 



* Strassburger, ZcIUhMuii;,' uml /clitlutiluiig, 1878, ]il. ii. ligs. 73-75. 



