Miscellaneous Uses 295 



by Krauss et al (1948). The application of auxins at the time of fruit- 

 set or during early stages of fruit growth resulted in increases in size 

 running from ten to thirty-five per cent in each of these fruits. 



It is difficult to distinguish the effects of auxins on maturation 

 and coloration from their effects on alteration of fruit size. In many 

 instances both effects are obtained simultaneously in the same fruits. 

 The first report of hastened maturation was made by Gardner et al 

 (1940) who observed increased coloration and maturity in apple 

 fruits which had been sprayed with auxins to prevent pre-harvest drop. 



The physiological basis for the effect on fruit size appears to be 

 two-fold, the auxin brings about an increased growth rate and an 

 alteration of the time of maturity of the fruit. 



In almost every reported instance the application of auxins to 

 young fruits of the spe( ies listed above results in an immediate in- 

 crease of the growth rate over that of the contiol. Clark and Kerns 

 (1943) observed that sprayed pineapples increased in weight over the 

 untreated controls very soon alter the spray. They implied that the 

 gain in size was largely owing to this stimulation. Some data reported 

 by Marth et al (1950) on the effects of auxins upon the growth of 

 peach fruits indicate that an inunediate growth increase was obtained 

 even though the final size was not increased. It will be remembered 

 at this point that in the discussion of parthenocarpy in chapter XI 

 it was observed that tomato fruits set with auxins showed a more 

 rapid growth rate in the first five days after auxin application (Single- 

 tary, 1950). 



The acceleration of Iruit growth by auxins is apparently the 

 greatest in cases where the fruits experience periods of retarded 

 growth as in the case of the fig. In figure 122 the normal growth rate 

 for the fig is plotted, showing two periods of rapid growth with a 

 period of relatively slow growth in between. The application of 

 2,4,5-T at the beginning of the slow phase in growth resulted in matu- 

 ration of the fruit in fifteen days instead of the sixty-five days normally 

 required. It has been suggested by Zielinski et al (1951) from their 

 work with prunes that such growth effects are caused by the rein- 

 forcing of low auxin levels in the fruit. A similar hastening effect is 

 obtained with apricot fruits (Crane and Brooks, 1952). The apricot 

 has three phases of rapid growth, and if 2,4,5-T is applied during the 

 slower phases the fruits may be brought to maturity about two weeks 

 early and with an increase in final fruit size. 



Fruits which do not show cyclic fluctuations in growth may still 

 obtain size increases with the application of auxins. An example of 

 this is the strawberry which yields small increases in fruit size when 



