THEORETICAL CONCLUSIONS 419 



3. The mature embryo sac may contain a maximum of 16 nuclei 

 and a minimum of 4, the commonest being the 8-nucleate condition. 



4. The functions of the sac seem to be adequately performed, 

 whatever the number of nuclei entering into its composition and 

 whether it is derived from one, two, or four megaspores. 



5. The gametic characters are not confined to the egg cell alone; 

 sometimes the synergids, and less often the antipodal cells also, 

 may give rise to embryos. 



6. The polar nuclei, although usually two, frequently exceed this 

 number, and sometimes there is only one polar nucleus. 



7. Endosperm formation is postponed until after fertilization and 

 the primary endosperm nucleus shows varying degrees of poly- 

 ploidy depending on the number of nuclei which have entered into 

 its composition; one of the fusing nuclei is a male gamete. 



Turning now to Gnetum : 



1. As in the angiosperms, the gametophyte may be monosporic, 

 bisporic, or tetrasporic. 3 



2. The number of divisions taking place after megasporogenesis 

 is considerably less than in most other gymnosperms. At the con- 

 clusion of the divisions there are usually about 512 nuclei, but 

 sometimes there are twice as many and rarely only half the number. 



3. The nuclei become distributed at the periphery of the cell, 

 leaving a large vacuole in the center. No compact tissue is formed 

 except in the chalazal portion of the gametophyte. 



4. Archegonia are absent and apparently every nucleus in the 

 upper part of the gametophyte is a potential gamete. One or a 

 few of the nuclei increase in volume and become surrounded by 

 dense cytoplasm to form the eggs. 



5. Fertilization may occur either in the free nuclear stage or 

 after partial cell formation. 



6. A certain amount of storage tissue (endosperm) is often pres- 

 ent at the time of fertilization, but the bulk of it is formed only 



3 Lotsy (1899) states that in G. gnemon the mother cell divides into two cells, 

 each of which may give rise to an embryo sac, i.e., the development is bisporic; 

 Thompson (1916) reports that the development is monosporic; and Fagerlind (1941) 

 writes that in G. gnemon var. ovalifolium all four megaspore nuclei take part in 

 the development, i.e., the embryo sac is tetrasporic. The reports of Lotsy and 

 Fagerlind of course need confirmation 



