90 



MORPHOLOGY OP ANGIOSPERMS 



off by walls, showing no tendency to migrate toward the posi- 

 tion of antipodal cells. This remarkable history is regarded by 



Campbell as repre- 

 senting a primitive 

 phase of the embryo- 

 sac of Angiosperms ; 

 a view from which 

 Johnson dissents, and 

 in a more recent pa- 

 per 114 he shows that 

 in the allied Piper 

 and HecTceria the 

 eight-nucleate stage 

 of the embryo-sac is 

 reached in the usual 

 way. It is tempting 

 to connect such a sac 

 as that of Peperomia 

 with such as that of 

 Gnetum, and theo- 

 retically it repre- 

 sents what one might expect to be an earlier condition of 

 the female gametophyte among Angiosperms ; but Johnson in- 

 fers from the testimony of Piper and Heckeria, just referred 

 to, that this particular sac of Peperomia is specialized rather 

 than primitive. 



In Gunnera, according to Sclmegg, 103 there is no polarity 

 in the early stages of the embryo-sac, and the nuclear divisions 

 are not simultaneous but irregular, so that there is no definite 

 eight-nucleate stage of the sac. Before fertilization there are 

 " at least " eight nuclei, and very commonly one or more of the 

 nuclei divide so that nine or ten and sometimes even sixteen 

 nuclei are found (Fig. 39); in which case, as in Peperomia, 

 the primary endosperm nucleus is formed by the fusion of a 

 considerable number of nuclei. A similar lack of polarity has 

 been observed in Tulipa sylrestris by Guignard, 890 and in Tril- 

 lium grandiflorum by Ernst 110 ; in the latter case at least two 

 of the nuclei of the eight-nucleate sac have been known to di- 

 vide, giving rise to a sac witli ten nuclei. 



In the embryo-sac of Juglans rer/iu Xawaschin 3S has indi- 



Fig. 89. — Gunnera. A, embryo-sac with nine nuclei, 

 showing no polarity. £, later stage showing sixteen 

 nuclei ; s, synergid nuclei ; 0, oosphere nucleus ; near 

 center, a group of six nuclei fusing to form endosperm 

 nucleus; near base, seven antipodal nuclei. — After 



SOHNEOG. 103 



