ith 



362 BOTANICAL GAZETTE [may 



benzidine for 12 to 24 hours. The formation of colors in distinct 

 zones is fully as striking as in the case of a-naphthylamine. As 

 before, the root cap does not produce oxidation products, the primary 

 meristem is marked by a narrow band of brown color, the zone of 

 elongation is practically uncolored, whereas the portion of the root 

 just above the zone of greatest elongation is entirely colored blue- 

 black or black by the oxidation products. 



Solutions of vanillin and vanillic acid act in much the same manner 

 as those of naphthylamine or benzidine, but the concentrations re- 

 quired to demonstrate the oxidizing power of roots are quite strongly 

 toxic. 21 Both substances are converted by the oxidizing action of 

 the roots into a purple insoluble dye which stains the surface of the 

 roots in the manner previously described. The concentration of 

 vanillin in the solution most favorable for showing oxidation iT 

 wheat plants lies between 250 and 500 parts per million. A solution 

 of this concentration will demonstrate the oxidizing power of the 

 roots before the plants become seriously injured. To demonstrate 

 the oxidizing power of roots with vanillic acid, a solution of the 

 latter containing 25 to 50 parts per million should be used. 



Esculin is another chromogen belonging to this class, bu \vas» 

 found to be less suitable for this work. Esculin solutions, w en 

 freshly prepared, exhibit a blue fluorescence. After plant roo^b 

 have grown for a few days in such a solution, the blue fluorescence 

 is lost, and the roots themselves are colored yellow as a res 0^ 

 their oxidizing activity, the dye formed being insoluble and remal ™ 

 upon the surface of the roots where the greatest oxidation occurs. 



The concentrations necessarv to demonstrate the oxidizing po* 



ii« nn A nrr eventually 

 roots range from 500 to 1000 parts per million, ana art 



quite toxic to wheat plants. [ te d 



The second class of chromogens, viz., those which are con^ ^ 

 into soluble coloring matters, are in many respects more us £ ^ 

 oxidation studies than those belonging to the first class, e ^ 

 the intensity of the color, and hence the amount of onda ^^d 

 be quantitatively expressed. The substances belonging to ^^ 

 class which have been employed in this study are pheno p 



" Bur. Soils, U. S. Dept. Agric. Bull. No. 47- I0 °7 

 1: 33- *9°7- Bot. Gazette 45:73. 1908. 



Proc. Soc. Biol Chem 







