104 Otis F. Curtis 



The injurious effects resulting from the presence of organic matter 

 may not be hmited to those directly correlated with increased carbon- 

 dioxide or decreased oxygen content. It is very probable that there are 

 certain toxic, partially oxidized substances formed which are directly 

 injurious. In fact, evidences of fermentation and putrefaction were 

 shown by tests for alcohol and by the odor of the solution. Aside from 

 the direct effect of increased carbon-dioxide and decreased oxygen on the 

 respiration of the cuttings, the same condition would tend to increase 

 the production of these partially oxidized toxic substances in the medium. 

 Stimulation by manganese may not be directly due to its effect on respira- 

 tion of the cutting, as discussed in the preceding pages, but it may be indi- 

 rectly due to the reduction of toxicity as a result of more complete oxidation 

 carried on either by the cutting or by the microorganisms, or possibly in 

 the solution independent of either. Loew (Loew and Sawa, 1902-03) has 

 suggested a similar role for manganese — that it serves to carry on oxida- 

 tion to completion, thereby preventing the accumulation of toxic, par- 

 tially oxidized by-products. 



COMPARISON OF THE EFFECT OF POTASSIUM PERMANGANATE WITH THAT 

 OF OTHER MANGANESE COMPOUNDS, AND ALSO WITH THAT OF IRON, 

 OF ALUMINIUM, OF BORON, AND OF PHOSPHORUS 



Since manganese dioxide seemed to be one of the active principles in 

 stimulating root growth in the experiments thus far cited, experiments 

 were made to determine whether this compound added directly to the 

 medium would have a similar effect. At the same time other compounds 

 were used which, according to the literature available, had under certain 

 conditions stimulated root growth in seedlings, or which, as in the case 

 of iron, were supposed to have some connection with oxidizing enzymes. 



Experiments with herbaceous cuttings 



The first experiment was made with tomato cuttings, since these root 

 very quickly and would give an idea as to the approximate concentra- 

 tions to be used. The stems were not of uniform size but care was taken 

 to distribute them equally. Duplicate cultures of five cuttings each were 

 set up. The roots were measured six days after the cuttings were started, 

 with the results shown in table 9: 



