A. E. MURNEEK 339 



aborted embryos. Eyster (25) has reported that when flowers were 

 sprayed immediately before or shortly after pollination with a weak 

 solution of naphthaleneacetamide, highly inbred self-sterile plants of 

 several species produced viable seeds. 



Endosperm and Its Role 



In detailed studies of embryo, seed, and fruit development considerable 

 emphasis has recently been placed on the endosperm (9). This 3n inter- 

 callary tissue between the new and old sporophyte provides the medium 

 suitable for the growth of young embryos. Usually its development 

 precedes that of the embryo. A failure in the necessary nuclear division 

 or function of the endosperm as a rule results in failure of embryo 

 growth. The endosperm increases rapidly during the early stages of seed 

 development and is digested and absorbed by the growing embryo. Its 

 role seems to be entirely nutritive. There is usually little or no endosperm 

 when the seed is mature, excepting where it has assumed the secondary 

 function of a storage organ. 



The important activity of the endosperm in nourishment and de- 

 velopment of the embryo of angiosperms has been summarized by 

 Brink and Cooper (1940) which may be paraphrased as follows: Since 

 the female gametophyte is exceedingly small in size and no endosperm 

 is formed till after fertilization, the ovule contains little or no reserve 

 food. The new sporophyte would be thwarted in development were it 

 not for the fact that fertilization initiates not only growth of the endo- 

 sperm but stimulates to active expansion the adjoining maternal tissues 

 (pollination as noted before, does it also). Originating as uninucleate 

 structures the embryo and endosperm must compete for food supply 

 with the adjoining well-established tissues. Success of the young seed 

 would seem to depend primarily on the endosperm as a nutritive agent 

 of the embryo to assist it in estabhshing its dominant position in the 

 ovule and ovary. Double fertilization appears to be the method con- 

 ferring upon endosperm the necessary power through physiological ad- 

 vantages of the hybrid condition. If during early development the 

 endosperm fails to remain dominant the surrounding nucellus or integu- 

 ments may outgrow it withholding or diverting the food supply from the 

 embryo. This results in starvation of the embryo and collapse of the 

 seed — the so-called somatoplastic sterility (17). 



Should one consider farfetched the suggestion that the synergids, 



