THE EMBRYO-SAC OF AGLAONEMA II3 



3. In A. siuiplex and A. tnodcstuiii the primary sporogenous 

 cell usually develops at once into the embryo-sac ; in y^. com- 

 imitatuni there may be a group of several large sporogenous 

 cells, which is probably the result of the division of a primary 

 sporogenous cell. A division of the primary sporogenous 

 cell is also occasionally found in A. modestuui. 



4. The growing embryo-sac soon destroys the outer tissue 

 of the nucellus, with the exception of the apical region, 

 which persists for a long time in A. simplex, but in A. 

 7nodestmn the young embryo-sac also destroys the apex of 

 the nucellus. 



5. \\\ A. coviuiutatHvi there is some evidence that the com- 

 plete embryo-sac may be the product of the union of several 

 sporogenous cells (megaspores). 



6. The first nuclear divisions in the embryo-sac in A. 

 simplex and A. modestum, and also in A. commutatum in 

 some cases, result in four free nuclei arranged in pairs. While 

 these are often placed at opposite ends of the embryo-sac, 

 this is not always the case. 



7. \n A. simplex and A. modestum only one of the upper 

 pair of nuclei divides, giving rise to the synergidse ; the other 

 becomes at once the nucleus of the egg-cell. 



8. The two chalazal nuclei remain undivided until after the 

 ^gg apparatus is complete, so that at this stage the embryo- 

 sac has but five nuclei. There is subsequently a division of 

 the lower pair of nuclei, but no nuclear fusion preliminary to 

 the first formation of endosperm, and no definite antipodal 

 cells are developed. 



9. No evidence of fertilisation was seen, and it is impossible 

 to state at what stage in the development of the embryo-sac 

 this occurs, if indeed there is any fertilisation. 



10. In A. pictum there were found in some cases what 

 looked like true antipodal cells, and a fusion of two polar (?) 

 nuclei precedes the endosperm formation. 



1 1. The first formation of cell walls in the endosperm occurs 

 after there are four free nuclei in the lower part of the embryo- 

 sac. The development of cellular endosperm proceeds from 

 the base of the sac to the apex, and the sac becomes soon 

 filled with a mass of endosperm cells. 



12. The first formed endosperm cells are usually smaller. 



