254 D. F. JONES. 



in no case produced a greater number of seeds than the number 

 of compatible pollen grains applied. In the other experiment 

 a constant white-flowered self-sterile plant was pollinated with 

 its own pollen. Several hours later pollen of a red-flowered 

 plant was applied. Abundant seed was secured and when grown 

 red-flowered cross-fertilized plants only were found. In both 

 these cases there was complete selective fertilization in favor 

 of the pollen from dissimilar plants. 



According to the results to be reported here a directly reversed 

 effect is obtained from mixed pollinations in maize. In many 

 trials the plant's own pollen has been more efficient in accom- 

 plishing fertilization than that from other individuals which 

 differ only in minor features. This same pollen which is less 

 effective when in competition with the plant's own kind of 

 pollen is fully able to function when not applied in mixtures. 

 The results are remarkable in view of the notable advantages 

 which cross-fertilization gives to the immediately resulting seeds 

 and the plants grown from them. The material used consisted 

 largely of self-fertilized strains which had been brought to uni- 

 formity and constancy and were considerably reduced in size 

 and vigor. In this material crossing is known to increase the 

 weight of seed within the same inflorescences as much as 50 

 per cent, in some cases. This greater amount of material is 

 laid down both in the embryo and endosperm, and is apparent 

 in the greater size of the seeds which show a higher specific 

 gravity together with more rapid maturation indicated by their 

 lower water content at the close of the growing period. A large 

 series of mixed pollinations show the ability of the cross-fertilized 

 seeds to germinate better by an average of 16 per cent. The 

 resulting plants start to grow sooner, develop faster, mature in 

 a shorter time and at the end far surpass their self-pollinated sibs. 

 The amount of heterosis shown by maize is possibly greater than 

 that displayed by any other plants in intra-specific crosses. 

 Production of grain has been advanced on an average of 180 

 per cent., height of plant 27, length of pistillate spike 29, number 

 of rows of spikelets 5 and number of nodes 6 per cent, in a study 

 of a large number of crosses between inbred strains (Jones, 1918). 



In spite of these great immediate advantages to be secured the 



