THE EMBRYO-SAC OF AGLAONEMA IO7 



are surrounded by a pretty definite mass of cytoplasm. As 

 we have seen, the egg apparatus may be formed also at the 

 base of the sac. By this time the embryo-sac begins to show 

 a distinct curvature (figs. 20 and 24), which later becomes 

 very pronounced and seems to be a constant character in 

 Aglaonema. 



Although many preparations were examined, in no case 

 could a satisfactory demonstration of the penetration of the 

 pollen tube or the fertilisation of the egg be made, and it is 

 quite impossible to say just at what period in the develop- 

 ment of the embryo-sac fertilisation occurs. Indeed, one is 

 almost forced to the conclusion that the development of the 

 embryo and endosperm goes on without fertilisation. For 

 some time after the endosperm formation begins the egg 

 apparatus remains apparently unchanged, and there is no sign 

 of a degeneration of the synergidse such as usually occurs in 

 cases of normal fertilisation. 



The development of the endosperm usually begins near the 

 chalazal end of the sac and proceeds towards the apex ; or it 

 may begin to develop on the concave side of the sac where 

 the young endosperm cells often form a somewhat compact 

 mass of small cells. Just when the first cell wall in the endo- 

 sperm is developed was not determined, but to judge from 

 the youngest specimens in which cellular endosperm occurred 

 (figs. 24, 25), it seems likely that after four free nuclei have 

 been formed the next nuclear division is accompanied by 

 the formation of a division wall. There is frequently found 

 in the A. simplex (figs. 24, 25) a discoid group of a few flat 

 cells with conspicuous nuclei. These are bounded by delicate 

 but evident cell walls, and in the undivided cavity of the sac 

 may be seen several free nuclei between which walls are 

 beginning to form. In the case figured (fig. 24) the egg 

 apparatus was lateral in position and placed close to the- 

 young endosperm cells, but there was no evidence of its 

 having been fertilised, the synergidae being intact and the 

 egg ((?) undivided. 



In A. simplex — and this is probably true also for A. modes- 

 tum and A. commiitatum — the endosperm formation is not 

 preceded by a fusion of free nuclei. In A. pictum, however, 

 as we hav'e already stated, there is a fusion of two nuclei into 



