Miscellaneous Uses 



297 



The acceleration of maturation phenomena in the fruit can 

 terminate growth before the fruits have reached full size. A clear case 

 of this premature maturation is found in the peach. If this fruit is 

 sprayed six or seven weeks before normal maturity, the fruits can be 

 harvested some two weeks earlier than normal (Weinberger, 1951), 

 but the growth rate is not maintained and the fruits are very small 

 (Marth et al, 1950). 



It seems generally true that the earlier the application of auxin, 

 the greater the maturation effect; however, associated with this more 

 rapid maturation is a greater frequency of distorted, undersized and 

 otherwise objectionable fruits. The effect of time of application upon 

 the maturation of peaches can be seen in figure 123. One might deduce 

 from the data reported in this figure and data of other authors as well 

 that fruits lose their sensitivity to auxins as maturity approaches. 

 Gerhardt and Smith (1948) have reported that auxins applied to apri- 

 cots, peaches, and pears after harvest had almost no detectable effect 

 at all. This was established on a more quantitative basis by South- 

 wick (1949) who demonstrated that post-climacteric apple fruits do 

 not respond to auxins in terms of respiration or any of the other 

 ripening phenomena measured. 



In some rather startling work on the nature of the ripening 

 process in avocado fruits, Millerd ei al (1953) have brought forth 

 good evidence that ripening of avocado proceeds as a function of the 



TIME OF APPLICATION 

 (Days before normal picking) 



Fig. 123. The relative effectiveness of sprays of 2,4,5-trichlorophenoxyacetic acid 

 (from 10 to 40 mg./l.) applied at various stages of development in hastening 

 maturity of peaches (data of Weinberger, 1951). 



