THE EMBRYO-SAC OF AGLAONEMA 1 03 



union of several megaspores. A very similar condition of 

 affairs was found in the genus Nephthytis (Campbell, 6). 



Mottier {loc. cit.) found in Ariscenia tripJiyllum a regular 

 division of the primary sporogenous cell into four megaspores, 

 the divisions being longitudinal, and one of these cells eventu- 

 ally develops into a typical embryo-sac, while the others are 

 destroyed in the usual way. 



Gow {loc. cit.) found a similar condition of things in 

 Spathyevia, except that in this case the embryo-sac was 

 developed from the lowermost of a row of three megaspores. 

 In both A. coinnmtatum and Nephthytis, however, all of these 

 megaspores seem to develop to a greater or less extent. In 

 the two species collected in Java, A. modestuin and A. sim- 

 plex, in most cases the primary sporogenous cell forms at once 

 the young embryo-sac, and this is the case also sometimes in 

 A. commutatuin. Exceptionally in A. modestuin there may 

 be a division of the primary sporogenous cell comparable to 

 that of Spathyema (PI. I. fig. 5). 



The usual type of A. simplex and A. modestnm is shown in 

 figs. 3 and 4. 



The embryo-sac mother cell is surrounded on all sides by 

 three layers of nucellar cells. The large and conspicuous 

 nucleus shows the usual structure, and has a single large and 

 conspicuous nucleolus. Nuclear divisions were not found at 

 this time nor in the earlier stages when presumably the reduc- 

 tion division occurs. Unfortunately it must remain uncertain 

 for the present when this takes place in Aglaonema. 



The young embryo-sac increases in size rapidly, encroaching 

 upon the adjacent cells of the nucellus, which, except for its 

 apex, is completely destroyed, so that the young embryo-sac 

 is practically in direct contact with the inner integument, and 

 only the conical apex of the nucellus persists as a cap covering 

 the apex of the embryo-sac. 



In A. commutatuin and A. simplex th.\s terminal cap persists 

 for a long time ; but in A. modestum the young embryo-sac 

 becomes very large before the first nuclear division occurs 

 and grows upward, quite destroying the apical portion of 

 the nucellus, so that it apparently terminates the nucellus 

 (PI. II. figs. 28 and 29). In this species one preparation 

 showed what looked like a second embryo-sac (fig. 28, e.s. {}) ) 



