Fruit Development as Influenced by 

 Growth Hormones 



FELIX G. GUSTAFSON 



THE production ot fruits is ordinarily associated with pollination 

 and fertilization, and it is almost axiomatic that if there is no 

 pollination there is no fruit setting. In many parts of the country 

 orchardists, to insure fruit setting, have gone as far as to distribute 

 beehives in their orchards during the blossoming period. In spite of this 

 common relationship between fruit setting and pollination and fertiliza- 

 tion we find that there are numerous instances in which fruits are pro- 

 duced without fertilization, and not even pollination is necessary in 

 some cases (lo). These fruits are seedless either because of lack of fertiliza- 

 tion or because the young embryos aborted leaving only tiny nutlets 

 as a reminder of fertihzation. Some of our so-called seedless grapes are 

 of the latter type (19), whereas the navel orange is illustrative of the 

 former situation, where not even pollination is necessary (25). 



Most seedless or parthenocarpic fruits, as they are technically called, 

 are probably produced as a result of pollination without fertilization. 

 It was as a result of the production of seedless fruits in infertile crosses 

 in Oenothera that the writer became interested in the subject. It was 

 reasoned that if the mere pollination stimulated the ovary to grow into 

 a fruit there must be transferred a stimulus either from the pollen or the 

 pollen tube to the ovary, and accordingly, several experiments were 

 set up to test the idea, Laibach (15) and Thimann (23) had found that 

 pollen contained growth hormones or auxin. If pollination without 

 fertilization can cause the ovary to develop into a fruit, and pollen con- 

 tains auxin, why not supply synthetic hormone directly to the pistil.? 

 That was done, and in 1936 (5) the writer succeeded in producing seedless 



