172 



D. F. JONES. 



from pollen mixture number i. The cross-fertilized seeds stand 

 out unmistakably on both plants, but are few in number. 



The data which show that this selective action is due in part, 

 at least, to differences in rate of pollen-tube growth, are arranged 

 in Table II. The total number of seeds in the top and bottom 



TABLE II. 



THE DISTRIBUTION OF CROSSED SEEDS IN MAIZE INFLORESCENCES RESULTING 



FROM MIXED POLLINATIONS. 



halves of the inflorescences, as divided arbitrarily before shelling, 

 are roughly equal. The number of cross-fertilized seeds per 

 hundred of all seeds is more in those seeds which resulted from 

 the shorter lengths of pollen tubes. Only one exception is noted, 

 and here there were only six crossed seeds in a total of over four 

 thousand. In all the others, positive differences are shown, but 

 these, however, are not large, so that one cannot be sure whether 

 or not the inequality in fertilization is due entirely to differences 

 in the rate of pollen-tube growth. Corroborative evidence has 

 been furnished by Miller (1919), who has observed that many 

 pollen tubes may start to grow down the style of maize, but in 

 about 100 examinations only one tube was seen to reach the ovary 

 cavity in every case. 



A similar selective action favoring the plant's own pollen has 

 been found with cotton. Balls (1919) put an equal quantity of 

 pollen of two distinct cultivated types of this plant (Gossypium) 



