190 Auxins in Agriculture 



It is not clear whether the acid conditions are superior because of the 

 relative abundance of anions or of undissociated molecules or alter- 

 natively because of a more ready entry by the auxin into the cell. 



Advantage was taken of the superior effectiveness of acidic solu- 

 tions of auxins by Lucas et al (1948), who buffered auxin spray prepa- 

 rations at an acid pH and observed that the spray was more effective. 

 Hard water with its rather alkaline condition has been reported to be 

 quite detrimental to the effectiveness of an auxin spray (Burg et al, 

 1946; Zussman, 1949). 



In weighing out the crystalline auxin, care should be taken that 

 the water of crystallization is accounted for in the weight. This is par- 

 ticularly important in the case of the sodium salt of naphthaleneacetic 

 acid, for Gortner (1952) has shown that an error of 35 per cent in 

 weight can be introduced if one does not take into account this pos- 

 sible error. In humidities ranging from 30 per cent to 90 per cent, 

 four molecules of water are taken up by each molecule of the sodium 

 salt, increasing its molecular weight from 208 to 280. At higher humidi- 

 ties, even more water is taken up. The potassium salt takes up one 

 molecule of water under similar conditions, and the free acid takes 

 up none. 



Impurities in the crystalline auxin preparation can distort experi- 

 mental results. This is particularly true if a technical grade of auxin 

 is used. Hansen (1951) has shown, for example, that technical meth- 

 oxone (2-methyl 4-chlorophenoxyacetic acid) contained as much as 

 53 per cent of other auxins and toxic materials. Even recrystallized 

 2,4-D of analytical grade contains quite large amounts of 2,4-dichloro- 

 phenol, a compound which is strongly active in uncoupling oxidation 

 from phosphorylation in the manner of dinitrophenol, and also in 

 activating indoleacetic oxidase (Goldacre et al, 1953). The significance 

 of agents of this sort was discussed briefly in chapter VIII. 



Some difficulty is commonly encountered in getting the crystalline 

 auxin directly into an aqueous solution. To facilitate this step, a few 

 milliliters of ethyl alcohol are often used to dissolve the crystals, and 

 then large amounts of water are added to bring the solution up to 

 volume. Three or four milliliters of alcohol will be sufficient to dis- 

 solve one tenth gram of crystalline indoleacetic acid. An alternative 

 method is to dissolve the crystals in a few milliliters of concentrated 

 NH4OH, then dilute to volume and neutralize with a mineral acid. 



In cases where very high concentrations of auxins are needed, 

 organic cosolvents are commonly used with water. For example, in 50 

 per cent alcohol one can successfully dissolve at least ten times as 

 much 2,4-D as could be dissolved in water alone. 



