



66 BOTANICAL GAZETTE [may 



the necessity of comparing a solution strongly tinged with yellow 

 against a solution which contains little or no yellow tint. In any two 

 solutions to be estimated the tints of yellow should not be greatly 



different. 



Leuco-rosolic acid is another reagent w r hich is useful for demon- 

 strating the oxidizing power of plant juices 28 and plant roots. When 

 a few cubic centimeters of a slightly alkaline, colorless solution are 

 added to a culture containing plants, the leuco-rosolic acid is oxidized 

 back to rosolic acid, the change being shown by the appearance of 

 the red color. This reagent is not so generally useful as phenol- 

 phthalin and aloin, since it is more readily oxidized by mere contact 

 with the air, as well as being more difficult to prepare. 



PRELIMINARY EXPERIMENTS 



The first experiments were conducted for the purpose of ascer 

 taining some general facts concerning the phenomenon of oxidation 

 by the roots of seedlings, as well as to learn the methods best suited 

 for studying oxidation in soil extracts. The experiments of Raci- 

 borski dealt with plants growing under what may be termed pure 

 culture conditions, and those of Kastle were concerned with the 

 oxidizing power of plant extracts. 



In the first experiment, wheat seedlings 4 days old were placed 

 in solutions of a-naphthylamine having concentrations of 1, h 5> 

 and 10 parts per million, and in a solution of 5 parts per million 

 benzidine. The experiment was set up at 4 p. m. August 6, an 

 observations were made eighteen hours later. At the expiration 

 that time colors could be distinctly seen on the white surface of the 

 wheat roots. The roots in the solution of 1 part per million nap 

 thylamine were pale lavender ; in 2 parts per million they were pro 

 nounced lavender, except at the root cap ; in the 5 parts per mi 1 

 solution they were violet in the region occupied by the prima . 

 meristem, and in the region of the root hairs where growth of elonga- 

 tion occurs, while the root cap and a narrow zone just above e p 

 mary meristem were uncolored ; in the 10 parts per million solution 

 roots showed the same colors as in that of 5 parts per million, 

 roots in the solution of 5 parts per million of benzidine showed 



»» Kastle, J. H., Hyg. Lab., U. S. Pub. Health and Mar. Hosp. Serv. 

 17. iqo6. 





