SELECTIVE FERTILIZATION IN POLLEN MIXTURES. 



279 



POLLEN MIXTURE No. 20. 



POLLEN MIXTURE No. 21. 



POLLEN MIXTURE No. 22. 



PREVIOUS INVESTIGATIONS ON SELECTIVE FERTILIZATION. 



From the work of Kolreuter, Herbert, Gartner, Darwin, 

 M tiller, Knuth and others we are familiar with the phenomenon 

 of self-sterility in plants in which the individual's own pollen is 

 wholly incapable of functioning on the plant by which it is pro- 

 duced although perfectly developed and able to fulfill its duties 

 when brought to other plants of the same species. Numerous 

 investigators have been giving attention to this problem in recent 

 times. East and Park (1917) have made a noteworthy contribu- 



