368 BOTANICAL GAZETTE [may 



The two cultures of poor soil gave readings of 40 and 42 divisions 



No 



the 



two cultures of rich garden soil gave readings of 14 and 24 divisions 

 against slide No. 4 (Lovibond system). Averaging the readings and 

 comparing the intensity of the colors, the oxidation in the poor lawn 

 soil and in the rich garden soil stands in the ratio of 1 to 4, or more 

 exactly as 19 to 82. This result indicated that a procedure based 

 upon this method will give satisfactory quantitative results. 



This method was further tested by another experiment in which 

 different beneficial treatments were applied to an extract of the 

 unproductive soil used in the last experiment. The results of the 

 last experiment showed that the oxidizing powers of plants growing 

 in solutions of different physiological properties vary considerably, 

 but left the question open as to how much of the oxidation result 

 might be due to plants and how much to the solution. In the pres- 

 ent experiment, therefore, two of the four bottles in each set of solu- 

 tions were left implanted, and their oxidizing powers measured along 

 with those of the solutions which contained plants. The treatment 

 employed consisted in adding fertilizer substances in the form of 

 pure chemicals. Calcium carbonate was added at the rate of 



2000 



and sodium nitrate at the rate of 50 parts per million. The cultures 



grow 



of 



amount of water transpired by each culture was ascertained and 3 

 of a freshly prepared phenolphthalin solution added to each bottle. 

 The color of the phenolphthalein was brought out by adding a few- 

 drops of strong alkali to each culture, and the intensities of the differ- 

 ent solutions were compared in the colorimeter. Table I presen s 

 the figures which give the relative amount of oxidation in the pi ante 

 and unplanted solutions. When the phenolphthalin solution v 

 added to the culture jars, the same quantity was added to a jar 

 distilled water, which served as a control upon the oxidation mciden^ 

 to contact with atmospheric oxygen. The color intensity of the contro 

 was determined and subtracted from each of the other readings. 



The plants used in this experiment were quite young, and the exper 

 iment was only continued for four days, a period rather too 

 for the maximum oxidation effect, as shown by subsequent expei^ 

 ments; nevertheless, the results show that the different treatmen 



short 



