218 Atkinson. 



into flower. It was a typical nutella. During the summer of 1913 

 a much larger number of hand pollinations were made. Several in- 

 florescences were also protected by covering with paper bags. In no 

 case did seed develop. A large number of hand pollinations were again 

 made in 1914, using not only nutella (n X p) but nutella (p'X n). No seed 

 was obtained. 



The sterility of the blend hybrid {nutella) is not due to sterility 

 of the pollen or Qgg cells. Flowers which are unprotected, if visited 

 by bees which have access to parents or other species, growing in 

 proximity, set an abundance of viable seed. When hand pollinated, 

 using pollen from either parent, from hyhrida pycnella, hyhrida tortuosa, 

 from Oe. grandifiora, LamarcJciana, and some other species, an abundance 

 of viable seed is formed. The pollen is well formed, showing a very 

 small and no greater percentage of poor grains than either of the pa- 

 rents. It is effective when placed on the stigma of either parent, on 

 hyhrida pycnella and hyhrida tortuosa, on Oe. grandifiora, LamarcJciana 

 and other species. 



The cause of the sterility of hyhrida nutella, therefore, has not 

 been determined. But it may be due to a lack of correlation in certain 

 of the physiological processes among the blended "factors", or characters, 

 inherited from the two parents. Or it may be due to a lack of blending 

 among some of the homologous characters, structures or physiological 

 processes or parts of the inflorescence. If a complete and equal blen- 

 ding of all homologous "characters" of the inflorescence took place, it 

 may be that the reproductive processes would present as high a degree 

 of efficiency as the vegetative processes have. That the phenomenon 

 of blending homologous characters does not take place among all the 

 homologous characters of the inflorescence is shown by the petals which 

 are far more like those of nutans than of pycnocarpa. The blending of 

 certain parental characters in the inflorescence, the taking over of others 

 in their entirety from one parent with the exclusion of their homologues, 

 and possibly the incomplete blending or unequal sharing in the union 

 of others may produce an organization ineffective for the reproductive 

 processes. Certain of the "qualities" or properties combined in the egg, 

 or pollen, or both, may lack the reciprocal influences necessary to a 

 union of sperm and egg, although sperm and egg are effective in other 

 combinations. It is also possible that certain physiological properties may 

 retard the growth of the pollen tube when the flowers are selfed, but 

 may not be effective against the growth of the tube from foreign pollen. 



