THE EMBRYO-SAC OF AGLAONEMA IO9 



The absence of definite antipodal cells, in most cases at 

 least, is noteworthy. The behaviour of the antipodals in the 

 AracecC shows much variation. In Lysichiton, for example, 

 there are at first the usual three antipodals, which subse- 

 quently undergo great enlargement and division so as to form 

 a large mass of tissue, which evidently supplements the endo- 

 sperm. In Spathicarpa they become enormously enlarged 

 and sometimes, though not always, there is a slight increase 

 in the number. A great enlargement was observed by Hof- 

 meister in Arum orientale, and probably other instances 

 could be found among the Araceoe. The absence of definite 

 antipodals in Aglaonema is also true for Nephthytis liberica, 

 which in many respects resembles the type of A. commutatum. 

 The behaviour of the antipodal cells in the Araceai confirms 

 the view that the antipodals and endosperm are both forms 

 of gametophytic tissue which serve much the same purpose 

 and may to a certain extent replace each other. 



The Embryo. 



Embryos in various stages of development were found, but 

 as a differentiation of the organs takes place only after the 

 embryo has reached a large size, the study of the young 

 embryo does not throw any light upon the origin of the 

 organs of the young plant. 



In most of the earlier stages met with, i.e. single-celled or 

 two-celled embryos, there was no indication of any degenera- 

 tion of either of the synergids, nor could a pollen tube be 

 satisfactorily made out. In a few cases there was some slight 

 evidence of degeneration in the synergids, but this was not 

 conspicuous, and in no case was there certain evidence of 

 the penetration of the pollen tube. It certainly looks as 

 if the development of the embryo might proceed without 

 fertilisation. 



Fig. 32 shows the appearance of the egg apparatus in 

 transverse section from an embryo-sac of A. simplex. The 

 egg cell had divided into a two-celled embryo, but the two 

 synergidae were still in a perfectly normal condition. In this 

 case the embryo was at the apex of the sac. In the basal 

 region of the same sac (fig. 33) there were about ten nuclei 

 and the endosperm formation had begun. 



