Chemical structure and biological activity 



A-gaps {tif,^) and of the molecular effect c,^ of a single molecule. The expres- 

 sion in brackets states again the probability with which such an A-gap gets 

 occupied by the entering molecule. 



Finally, the fourth term describes the extent to which molecules of the 

 entering growth regulator oust the molecules of the natural growth regulators. 

 Exactly the same considerations as in the case of the second term lead to the 

 conclusion that the molecular effect produced by one replacement has to be 

 ^h — ^7t' ^^'^^ therefore, B^ is generally negative. An exception, however, is 

 present when a strong effective component of the natural regulators is 

 applied. In this case, B^ may be positive. The bracket- term furnishes again 

 the probability with which one A-gap, naturally occupied, gets filled by the 

 replacing foreign molecule. 



Figures 1-3 show the agreement of the theoretical function with the experi- 

 mental data for a strong effective component of the natural growth regulators 

 (indoleacetic acid) promoting cell elongation growth, for a foreign promoting 

 substance (a-naphthylacetic acid) and for an inhibiting substance (eosine). 

 Obviously, the absence of the first term means that the growth regulator 

 is an inhibiting substance, and mathematically it says that either the mole- 

 cular effect c„, or k^^, is equal to zero. In the latter case one has to suppose that 

 the second term has to become zero too, because the probability of replace- 

 ment k',^, is to be assumed as smaller than the probability of occupation k^, 

 of an empty gap. If the second term is present, A^ is proportional to c,^; 

 this consideration makes it possible to set in proportion the r„, and c,, of the 

 different substances, as I showed in my paper last year. Furthermore, one 

 can calculate the proportion between the probabilities /:„. and k^ and finally 

 the proportion of the number of gaps n^„„ and «,,,^. Subsequently, one can 

 separate the growth-promoting and inhibiting components in regard to the 

 effectiveness of the regulating substances. 



Briefly repeating the results referred to last year, I was able to calculate 

 the proportion of the promoting effect {X) and the inhibiting effect ( Y) of 

 differently acting substances. The result for the promoting effect was: 

 A'j (indoleacetic acid) : ^2 (oc-naphthylacetic acid):Z3 (4 : 6-dinitro-ori/^o- 

 cresol) : Z4 (pentachlorophenol) : X^ (eosine) : A^g (dinitro-ori/?o-i-^(:. butyl- 

 phenol) = 1:0-33: 0-97: 0-16: 0:0; 

 and for the inhibiting effect: 



7i : Y^ : Y.^ : 7^ : 7^ : 7^ = 1 : 32 : 2350 : 794 : 74900 : 1640. 



The complex effect of growth promotion expressed in terms of Z, = X^jY^ 

 is thus given by the relation 



Zi : Z2 : Z3 : Z4 : Z5 : Zg = 1 : 0-01 : 0-0004 : 0-0002 : : 0. 



In my opinion, a classification of the different growth regulators is only 

 possible if one analyses the concentration-action curves and compares the 

 different components which yield the complex phenomena one can observe. 

 One might object to this on the ground that the shape of the function derived 

 from the hit-theory will fit in with any experimental results, but I have shown 

 in my previous paper that the different parameters of the function are limited 

 by different rules extracted from the experimental investigations carried out 

 by H. Linser (1954). The only source of unreliability in the calculation of 



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