chapter iv 

 for:mation and occurrence of auxins 



A. The Formation of Auxin in the Plant 



We have seen that in Arena the auxin produced in the 

 tip is one of the principal factors controlhng growth. The 

 question therefore arises, how far can the findings on Arena 

 be appUed to the general phenomenon of growth in the plant 

 kingdom? Although auxin has been found in the green alga 

 Valonia (van der Weij, 1933, 19336), and in fungi (see IV E, 

 VII C), our knowledge of those growth correlations in lower 

 plants which may be controlled by special substances is too 

 limited to allow any comparison with higher plants. Our 

 first consideration must therefore be, how general is the 

 production and occurrence of auxins, and in what parts of 

 the plant are they produced? 



First of all it must be pointed out that there are a number 

 of chemically different auxins, whose physiological action is, 

 except for quantitative differences, the same. We shall 

 make no attempt to distinguish between these here. In 

 those few plants which have been examined there is, how- 

 ever, e\'idence that the auxin present is auxin a (see VII D). 



There are two main methods for obtaining auxin from 

 plant parts. The first, and most used, is that of allowing 

 auxin to diffuse out into water or an aqueous gel. For this 

 agar is generally used. The method was first appUed by 

 Went to Arena coleoptile tips, but has subsequently proved 

 itself of general applicability to almost all auxin-producing 

 organs. In some cases the auxin so obtained may be in- 

 activated by enzymes diffusing out of the cut cells. That 

 such inactivation is a usual consequence of crushing tissues 

 was first shown by Thimann (1934) and later by the exper- 

 iments of van Overbeek (1935), Kornmann (1935), Fiedler 

 (1936), and Larsen (1936). The inactivation at cut surfaces 



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