I9 o9] SCHREINER & REED-OXIDIZING POWER OF ROOTS 365 



ai^ per cent, sodium chlorid solution and adding 5 CC of concentrated 

 copper sulfate solution. Almost immediately the straw-yellow solu- 

 tion begins to change to a permanent deep wine-red. The change is 



hastened by warming the solution. 



When experimenting with plant juices containing enzymes, there 

 appears to be a difference between the reactions to aqueous and 

 alcoholic solutions of aloin. As the result of experiments described 

 in detail in a subsequent section of this paper, it was found that an 

 aqueous solution of aloin is a better indicator of the presence of 

 oxidase, while an alcoholic solution of aloin is the better indicator 



of peroxidase. e . . 



Aloin, like phenolphthalin, should be added to neutral or faintly 

 alkaline culture solutions, and where quantitative results are desired 

 all solutions should be of the same degree of alkalinity. In all 01 

 wr wk aloin was added at the rate of ioo m * of aloin to 250" of cul- 

 ture solution. If actively growing seedlings are used in a very faintly 



amoun 



an hour or two, but the experiments should be continued for 12 to 

 20 hours for the final observation. When certain inorganic salts were 

 present in the culture solutions, the aloin red color was slightly moa- 

 ted. The addition of nitrates or previous treatment of the sou 

 extracts with an absorbing agent gave the oxidized aloin a purpii- 

 tinge, resembling that of fresh fuchsin solution. The presence 

 calcium carbonate gave a purer red color, resembling alkanna 



— 1 • 



cochineal solution. 



The fact that aloin is changed by oxidation from a hght yeHowto 

 » deep red solution makes it somewhat more difficult to ob.am 

 colorimetric readings than in the case of phenolphthahn, where me 

 >• a change from a colorless to a red solution. Neverthe fes, .U 

 Practical to use the colorimeter for measuring Vg'T*** ? 

 iMensitv of color in aloin solutions, by arranging the ■**■»" 

 *e order of their apparent color intensities, and usmg ea h soluUo 

 * as an unknown and then as a standard for the nex higher 

 ^ example, let No. t , the weakest color, be the --*■*££ 

 *4 No 2 is read. Then discard No. . ; set No. , £ •«£"* 

 **, and, using it as the standard, read No. 3- » ^ 



"»d as the standard for No. 4, and so on. In tms j 



