1908 COULTER— GNETUM GNEMON 



45 



ENDOSPERM 



A year later, the endosperm has destroyed all of the nucellar 

 tissue except a very small amount at the tip (figs. 6, 6a, yd), and it 

 is clearly differentiated into a central region of smaller, more compact 

 cells, and a more extensive peripheral region of larger and looser 

 cells. In destroying the nucellar beak, a curious result is observed. 

 The central region of the endosperm advances into the beak and 

 then spreads laterally (fig. 6). In the meantime the peripheral 

 region advances more slowly toward the beak, and as a consequence 

 a ring of nucellar tissue is pinched between two growing masses of 

 endosperm. The growth of the endosperm into the chalazal region 

 also results in pressure toward the beak, so that the pinched nucellar 

 tissue is under considerable pressure and becomes completely disor- 

 ganized. Under this pressure some of the adjacent endosperm cells 

 also become disorganized. 



In ovules of the preceding year, at the fertilization stage of the 

 embryo sac, a curious disorganization of some of the cells of the 

 nucellar beak was observed (fig. ja). Two transverse rings of cells, 

 several layers beneath the epidermis, begin to disorganize; later the 

 epidermis becomes involuted between the disorganized rings, resulting 

 in a deep groove around the nucellus. The epidermal cells remain 

 very vigorous in appearance, and when the endosperm develops into 

 this region the groove disappears. The cause and the significance 

 of this disorganization and of the temporary involution of the epi- 

 dermis cannot be suggested. 



EMBRYO 



Lotsy has described the entrance of pollen tubes into the embryo 

 sac, the fertilization of the free eggs, the excessive elongation of the 

 fertilized eggs to form suspensors, and the cutting-off of the embryonal 

 cells at the tip of the suspensor. Later stages in the development 

 of the embryo have been described by Bower, 4 but the intermediate 

 stages have not been observed. Fortunately our material from the 

 Philippines contained them, and revealed an unexpected situation. 



When the endosperm has become fully developed, its peripheral 



4 Bower, F. O., The germination and embryology of Gnetum Gnemon. Quart. 

 Jour. Micr. Sci. 22:278-298. pi. 2$. 1882. 



