Self Sterility and Cross Sterility in the Apple. 79 



It is true that certain differences may be noted dependent 

 upon the pollen supplied for a given cross. These differences 

 are not in immediate relation to the variety of pollen supplied, 

 but depend upon complex factors which will be analyzed in sub- 

 sequent publications. Furthermore the effect of the crosses 

 may be toward increased color in one cross and decreased color 

 in another, etc. So far as the effect on the fruit is concerned it 

 is absolutely safe and advisable to plant two varieties of dif- 

 ferent color, shape, etc. together. A red apple will be just as 

 red if pollinated with pollen from a green variety as if pollinated 

 with a red pollen variety. Of course the seeds resulting from 

 such crosses will be different in the two cases, but the flesh or 

 marketable portion will remain unchanged. 



This conclusion would be expected from other independent 

 ■evidence taken from histological studies of the development of 

 the apple. The apple is like an enlarged branch of the mother 

 tree. It does not receive anything of a genetic nature from the 

 resulting union of the pollen and the ovule. It only acts like a 

 sack to protect the seed. It is all maternal in origin and would 

 therefore be expected to assume the maternal characters, size, 

 shape, quality and color, of the mother tree. 



If we look at the problem in the light of the preceding data 

 on the self sterility and the cross sterility of the different varie- 

 ties it is found that the number of fruit set from self fertiliza- 

 ion is so limited as to make it entirely likely that the large pro- 

 portion of the apples in commercial orcharding are the result 

 of cross fertilization. Thus in table 2, one of the best com- 

 mercial varieties, the Baldwin, matured on self fertilization 20 

 fruit out of 409 trials, a percentage of about 5. On cross fertili- 

 zation this variety produced good fruit in something over 50 per 

 cent of the crosses which were made. The Ben Davis variety 

 matured no fruit in Maine on self fertilization yet this variety 

 is capable of bearing a crop of a color and size consistant with 

 the best of the variety even though the majority of fruit must 

 have been formed by cross fertilization with a foreign pollen. 

 In view of what the investigations on the causes of self sterility 

 have shown in relation to the growth of the pollen tube it would 

 seem more probable that in the commercial orchard the percent- 

 age of fruit set from self fertilization would be considerably 

 below the percentage obtained in experimental work. Thus 



