SELECTIVE FERTILIZATION IN POLLEN MIXTURES. 257 



the value of the figures as it is the relative efficiency of each type 

 of pollen, when it is applied to its own and to foreign stigmas, 

 that is being investigated. 



In the preliminary experiments there were 18 pairs of plants 

 which produced seed as the result of the application of mixed 

 pollen. When these were counted and the deviations of the 

 proportions found from the closest perfect proportions were 

 obtained there were 12 mixtures which showed a deviation in 

 favor of the self-fertilized seeds and 6 in the opposite direction. 

 The results as a whole showed a tendency to favor the plant's 

 own pollen. This was somewhat unexpected so that it was con- 

 sidered worth while to investigate the matter more fully. 



The inbred material was so reduced in growth that the number 

 of seeds produced on one plant was not large enough to give the 

 results much weight. It was therefore decided to pollinate a 

 number of plants of two different self-fertilized strains with the 

 same mixture. Most of the strains used had been self-pollinated 

 for six generations or more, some as many as ten, so that the 

 plants within one strain were practically identical in hereditary 

 constitution. Pollen was collected from about the same number 

 of plants as the pollen was applied to. The two lots of pollen 

 were put together in a paper sack and thoroughly mixed by 

 shaking. This mixture was then applied to plants of the two 

 strains which supplied the pollen. It was desired to have from 

 ten to fifteen plants in each of the paired strains so as to give 

 from 1,000 to 2,000 seeds in each of the two parts of the propor- 

 tions but the flowers were not always ready at the right time 

 and some pollinations were failures for a variety of reasons so 

 that not as large numbers as desired were secured in every case. 



Every effort was made to prevent the entrance of undesired 

 pollen. The technique has been described and the amount of 

 experimental error due to contamination to be expected in 

 artificial pollination of maize has been considered previously 

 (East and Hayes, 1911). In the course of these experiments the 

 effects of extraneous pollen were seen in very small numbers 

 compared to the total number. This source of error could be 

 detected in the seeds when colors or other characters differing 

 from either of the strains used were brought in by the undesired 



