Neo-Mendelism 49 



maturity. At that point, however, it was claimed that 

 development would stop were it not for the stimulus of 

 pollination and pollen tube development. This stimulus 

 apparently causes the female gametophyte to continue 

 its development to the final stage of preparation for 

 the reception of the sperm. Sterile pollen might furnish 

 this stimulus as well as fertile. If then pollination by 

 sterile pollen has taken place and the female gametophyte 

 has been stimulated to its complete ante-fertilization 

 development, this development may continue in spite of 

 the failure of an effective sperm to arrive, and the result 

 might be an apogamous embryo. In some such way the 

 relation of apogamy to sterile pollen, resulting from 

 wide crosses, might be explained. 



This conception meets with many objections, so many 

 that they cannot all be discussed. The chief difficulty, 

 however, may be stated as follows. Is there any mecha- 

 nism for the transmission of a pollen stimulus to the 

 developing female gametophyte ? We know of none, 

 but neither can we explain the mechanism of the sensitive 

 plant in which there is obviously the transmission of a 

 stimulus. Furthermore we know from facts in connec- 

 tion with parthenocarpy that pollination stimulates 

 development as deep within the tissue as the ovule 

 itself, and it would be easy to extend this to the develop- 

 ment of the female gametophyte as well. 



All this is still a field of speculation, but in any event 

 the reason for East's contention that wide crosses 

 may give hybrids that reproduce apogamously is evi- 

 dent. Wide crosses give sterile pollen; sterile pollen 

 stimulates the development of the female gametophyte 

 but cannot effect fertilization; the result is apogamy, 



