CHAPTER XIII 



OTHER ACTIVITIES OF AUXINS 

 A. Auxin and Cell Division 



It was mentioned in Chapter II that the work of Haber- 

 landt and his students has shown that cell division in the 

 parenchyma of a number of plants is controlled by dif- 

 fusible substances, which are present in the phloem, and 

 which are set free from other tissues by wounding. Such 

 attempts as have been made to characterize these cell- 

 di\dsion substances chemically (Wehnelt, 1927; Jost, 1935a; 

 Bonner, 1936 and u; Umrath and Soltys, 1936) give no rea- 

 son to believe that they are in general identical with auxins. 

 On the other hand, there are some conditions under which 

 auxins certainly produce cell division. 



Thus, Jost (1935a) in studying the parenchyma of the 

 pods of Phaseolus — the material used by Wehnelt — found 

 that the cells could be induced to divide not only by bean 

 juice and other preparations, but also by indole-acetic acid. 

 However, this substance acted only at the very high con- 

 centration of 0.1 per cent in water, concentrations up to 

 100 times those present in the plant being completely 

 inactive. Further, the bean extract, containing only 0.5 per 

 cent dry matter, produced more divisions than the 0.1 

 per cent auxin solution. Since the physiological activities 

 of indole-acetic acid and the auxin of the plant itself differ 

 only in a very minor degree, it is clear that the powerful 

 action of bean juice cannot possibly be ascribed to its con- 

 tent of auxin, but must be due to another special substance, 

 probably active in high dilution. A somewhat lower concen- 

 tration of auxin, namely 0.01 per cent in water, caused 

 \'igorous cell division in the pith cells of the stem of Vicia 

 Faha, and in the subepidermal parenchyma of the cotyledons 

 of the white lupin. This concentration, however, is also 



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