EFFECTS OP CROSS-POLLINATION ON SIZE OF SEED IN MAIZE. 13 



In the resulting ear the two khids of seed were easily distinguished. 

 The pure seeds resulting from the first pollination were ])ure white, 

 while the hybrid seed resulting from the second })ollination were 

 yellow. Unlike the ears where mixed jjollen was used, the two kinds 

 of seed were not indiscriminately distributed. All the white seeds 

 were on the lower portion of the ear; all the colored were on the 

 upper portion. This segregation of the two kinds of seed must have 

 deprived the hybrid seed of any advantage that might be secured by 

 crowding weak neighbors, while the time which elapsed between 

 the two applications of pollen precluded the possibility of the 

 hybrid seed appropriating material in advance of the pure seed. 



The ear producetl 212 white, or pure, seeds and 161 that were 

 yellow, or hybrid. The average weight of the pure seed was 283 

 grams per 1,000. The average weight of the hybrid seed was 292.5 

 grams per 1,000, a difference of 9.5 ±1.06 grams, or 3.4 per cent. 

 The seeds on the lower portion of the ear are usually somewhat 

 larger than those on the upper ])ortion, a fact that should be consid- 

 ered in connection with the observed increase. 



CONFLICTING RESULTS OF PREVIOUS INVESTIGATIONS. 



As soon as the phenomenon of xenia came to be recognized, the 

 possibility that size might be among the characters thus affected 

 was perceived by a number of investigators; but, without some 

 method of mixed pollmation similar to that used in our experiments, 

 changes in the size of seed could only be measured by comparing 

 the average size of seed from hybrid ears with the average size of 

 seed in the parent variety. There is such a range of individual 

 variation in maize with regard to the size of seed that hybrid ears 

 would have to be produced in very large numbers to recognize any 

 but very large differences. Since h^d^ritl ears were secured only 

 through artificial pollination, their number was naturally small and 

 it is not surprising that the results were more or less contradictory. 



Thus Correns^ made a series of crosses between races with different- 

 sized seed and compared the weight of the hybrid and parent varieties. 

 He viewed the results, however, from the standpoint of the inheritance 

 of size as a character and paid little attention to the jjossibUity of this 

 being an uicrease due to crossmg as such. With the limited number 

 of ears which he secured it was hardly to be exj)ected that mcreases of 

 less than 25 per cent could be detected with certainty. In summa- 

 rizing his results on this pomt, he states that while the size of the seed 

 is not essentially changed by cross-poUhiation there is a slight uicrease 

 in weiglit. By the method of m'lxed pollination used in our experi- 

 ments differences averaging as low as 2 per cent are significant. 



' Correns, Carl. Bastarde zwischen Maisrassen, Stuttgart, p. 30, 81, 1901. (Bibliotheca Botanica, 

 Heft. 53.) 



[C'ii-. ]i!4] 



