Acceleration and Retardation of Abscission 



563 



100 



80 



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 en 



03 



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 Q. 



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Fig. 4. Retardation of abscission by proximal application of small amounts of gib- 

 berellic acid. Each line is the average of three experiments totaling 120 abscission 

 zones. 



o£ the branch or young fruit, rather than direct effects of gibberellic 

 acid on the process of abscission. 



In other investigations where no effect of gibberellic acid was 

 found, the results appear due, in some cases at least, to the limitations 

 of the experimental material. For example, the Coleiis petiole ex- 

 plants used by Brian et al. (5) abscised so rapidly that both untreated 

 and treated petioles fell before the first observation was made. Under 

 such conditions, of course, accelerated abscission was not detected, 

 although it could well have occurred. For exploratory experiments 

 on abscission, the plant material should be so grown or so selected 

 that the controls show a moderate rate of abscission, thus permitting 

 the detection of both acceleration and retardation. 



The anomolous stem abscission following proximal application 

 of 100 ^g. of gibberellic acid is of considerable interest in that abscis- 

 sion of stem stumps has not been previously reported in cotton. (How- 

 ever, abscission of weakened or injured branches is characteristic of 

 a few plant species.) The stem abscission observed here was somewhat 

 similar to the anomolous abscission of bean stems following appli- 

 cation of triiodobenzoic acid to the apical bud, described by Whiting 

 and Murray (11). These unusual types of abscission deserve further 

 physiological investigation. 



