EFFECTS OF CROSS-POLLINATION ON SIZE OF SEED IN MAIZE. 15 



from 5 to 18 bushels more per acre when strains were allowed to 

 cross-pollinate than when cross-])ollmation was prevented. 



Another idea suggested by the results of these experiments is that 

 increase in the size of the seed in the xenia generation may serve as 

 a means of determinmg in advance the hybrid combmations that 

 will produce vigorous and productive plants the following genera- 

 tion. Whether this proves to be the case or not, the results afford 

 additional reason for the use of first-generation hybrid seed; but 

 even where hybrid seed is not to be used, the planting of two varie- 

 ties in alternate rows may be found to increase the yields sufficiently 

 to warrant the additional trouble. 



As the increased size is evidently a manifestation of vigor, it may 

 be considered as a factor of adaptation, like the vigor of the first- 

 generation hybrid plants. It would seem especially desirable to take 

 advantage of this method of increasmg the yield in regions which do 

 not produce their own seed corn. 



CONCLUSIONS. 



The experiments reported m this paper afford definite evidence 

 that the crossing of two varieties of maize is followed by an increase 

 in the size of seed in the same year that the crossing is done. This 

 increase is not to be confused with the increased yields secured in 

 the year following, when the first-generation hybrid plants are grown. 



By mixing pollen of a white-seeded and a colored-seeded variety 

 and applying the mixture to the silks of the white-seeded variety 

 pure and hybrid seed are produced on the same ear. By vii'tue of 

 the xenia inheritance of seed color the two kinds of seed produced 

 imder identical conditions can be distinguished and compared. 



This method makes it possible to measure the immediate increase 

 from cross-pollmation much more reliably and accurately than can 

 be done in any expermients involving the comparison of seed pro- 

 duced on different plants. The results showed the hvbrid seed to be 

 heavier in every instance, the increase ranging from 3 to 21 per cent. 



[Cir. 124] 



