SELECTIVE FERTILIZATION IN POLLEN MIXTURES. 259 



Different characters were used in other mixed pollinations 

 which permitted even more positive classification than the single 

 character difference of yellow and white endosperms. Plants 

 with yellow sweet seeds were paired with white starchy plants. 

 Each strain brought in a dominant character. White starchy 

 plants of the pop or Zea mays everta type were used because the 

 clear corneous endosperm differentiates very clearly between 

 yellow and white. In the reciprocal cross the smooth opaque 

 seeds show up plainly contrasted with the wrinkled translucent 

 seeds. Similarly purple sweet and white starchy types were 

 paired. In a few cases the purple crossed seeds were not as 

 distinct as could be desired, but the error is certainly small. 

 These latter mixtures were made the past season and no plants 

 have been grown to test the reliability of their separation but the 

 writer is confident that the number of wrongly classified seeds, 

 if any, is not sufficient to alter the results, appreciably. 



In many inflorescences a few seeds were found which had 

 failed to reach a stage of development so that they could be 

 classified. Seeds at the tips of the spikes and where the seeds 

 were closely crowded were abortive. This introduces another 

 source of unreliability, that of selective elimination of zygotes. 

 Since crossing gives to seeds of maize an enormous advantage in 

 development, it can confidently be expected that as a rule more 

 of the self-pollinated seeds will be found among the abortions 

 than cross-pollinated. What we are attempting to study is the 

 relative fertilizing efficiency of different types of pollen grains. 

 But one can only arrive at this by counting the zygotes sometime 

 after fertilization has taken place. In the meantime a differential 

 destruction of zygotes may have taken place. This effect must 

 be considered in any organisms employed but because of the 

 short time which elapses between fertilization and the maturation 

 of the seeds, and from the fact that they develop in an exceedingly 

 favorable and uniform environment, maize is the very best 

 material the writer can think of in which this problem can be 

 attacked, especially when the numbers which can be obtained 

 are taken into consideration. All animals and those plants 

 which d3 not show zenia in the seeds have the objection that a 

 comparatively long time elapses between fertilization and suffi- 



