434 University of California Publications in Botany [Vol. 5 



pollination, artificial stigmatic fluids have been used, etc. In all eases 

 the flowers have fallen. The results of microscopical examinations and 

 pollen cultures have always indicated that no normal pollen was pro- 

 duced. Still it has always seemed possible that there might be a very 

 few normal pollen grains corresponding to the percentage of normal 

 ovules. That there is no such good pollen seems finally proved by the 

 above results which show that two to five stylar penetrations or fer- 

 tilizations are sufficient to inhibit flower-fall. If even one-half of one 

 per cent of the thousands of pollen grains applied to the stigma were 

 normally matured the flowers should have been retained upon the 

 plant. Genetic incompatibility seemingly need not be considered in 

 connection with this abscission evidence as to the pollen condition of 

 these hybrids because it should not be expected to interfere with pollen 

 tube growi;h and probably not with fertilization itself. 



In the table data are given in a few instances as to the position on 

 the placentae of the mature seeds. Thus some fragmentary evidence 

 is given on the question of "selective" fertilization. Hartley {loc. 

 cit.) states "That there is a close relation between the pollination of 

 one half of the stigma and the setting of seeds in the corresponding 

 half of the ovary is certain . . . ." No data are, however, given by 

 Hartley as to the position of the seeds resulting in his experiments in 

 w^hich small amounts of pollen were used. Our results indicate that 

 there is no selective fertilization from the point of view of position on 

 the placentae and that the particular embryo-sacs reached by the pollen 

 tubes is a matter of chance. 



Transmitted May S, 1918. 



