3 6 ° BOTANICAL GAZETTE 



[may 



most 



^^^ ■ — ^^r ^^ "^* ^m 



was conducted for 8 to 12 days before studying the oxidizing action 

 of the plants, but during the cloudy winter weather the time was 

 somelimes extended to 14 to 16 days. 



In addition to determining the oxidizing power of the plants 

 subjected to various treatments, their growth was estimated by 

 recording the green weight and transpiration of each culture. 20 



SUBSTANCES CAPABLE OF SHOWING THE OXIDIZING POWER 



Two classes of substances have been found useful in showing the 

 oxidizing powers of plant roots in solution cultures. The first class 

 comprises certain soluble chromogens, which yield, upon oxidation 



the plant roots, insoluble colored compounds mainly deposited 

 upon the surface of the roots. The oxidation is usually rapid enough 

 to produce marked results before the surface extension of the roots 

 perceptibly disturbs the zonal distribution of the colors. The second 

 class of chromogens consists of certain substances which give soluble 

 coloring matters as the result of the oxidizing action of the roots. 

 The oxidizing action may be shown by the change from a colorless 

 to a colored compound, or by a change from one color to another and 



distinctly different color. 



first class which have been used in 



this work are a-naphthylamine, benzidine, vanillin, vanillic acid. 

 and esculin. 



Alpha-naphthylamine is only slightly soluble in water, but con- 

 stitutes a good reagent for use in plant cultures because its coloriess 

 solution is non-toxic, or nearly so, to plants. When oxidized by the 

 roots of plants, or by reagents such as ferric chlorid or silver nitrate 





«-naphthylamine is converted into the insoluble, lavender- purple 

 oxynaphthylamine. When the oxidation is performed by the growing 

 roots of a plant, the oxynaphthylamine is deposited upon the surface 

 of the roots in characteristic zones, as already described by RAO- 

 borski (op. cit. 357). The root cap is slightly if at all colored; the 

 zone of primary meristematic cells immediately back of the root caj 

 is marked by a distinct narrow band of color; the zone of activcl; 



*° For a discussion of the value of these criteria the reader is referred to ^J 1 ^^ 

 Box. Gazette 40:178. 190,-; Tensex, Bot. Gazette 43:"- I0 °7; and bU 

 °f Soils, U. S. Dept. Agric. Bull. 47. 1907. 



