CHAPTER V 



Physiological and Anatomicdl 

 Effects of Auxin Applications 



In the preceding chapters attention has been given primarily to the 

 physiological functions of auxins as they occur naturally in plants. 

 The introduction of synthetic auxins into plants has furnished much 

 information concerning the physiological powers of auxins. Some of 

 these powers relate to concentrations of auxins which may occur 

 naturally, but more of them relate to unnaturally high auxin levels. 

 A knowledge of the physiological and anatomical effects of auxins 

 not only is valuable physiological information, but also has a strong 

 bearing on the intelligent application of auxins in agricultural re- 

 search. 



GROWTH EFFECTS 



After the discovery of the existence of growth hormones and the 

 subsequent finding that many chemical compounds were able to 

 stimulate growth in a similar manner, hope naturally arose that the 

 simple application of these growth regulating materials to growing- 

 plants might increase growth and productivity. Unfortunately, it was 

 fotmd that auxins sprayed onto plants had very little beneficial effect 

 on growth in general. Promotions were obtained only in stem elonga- 

 tion for a day or two after the spray was applied. Indeed, instead of 

 beneficial effects, spray applications were generally followed by such 

 undesirable consequences as epinastic bending of leaves, interference 

 with normal leaf development, and the formation of swellings and 

 adventitious roots. 



A rather striking exception to the virtual lack of stimulation in 

 growth found in most growth regulator applications to green plants 

 appears in the study of Mitchell et al (1951). They observed that the 

 application of hormone extracts from young bean fruits to bean 

 seedlings increased growth of internodes and leaves by more than 200 

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