Stimulation of Root Growth in Cuttings 113 



The explanation previously given for the effect of treatments with 

 potassium permanganate could be applied to the results obtained with 

 manganese dioxide. The lack of as marked stimulation by the latter may 

 have been due to the fact that the dioxide was not deposited in close 

 proximity to the living tissues, as it was in the treatments with potassium 

 permanganate. In this case the possible oxidizing compounds other than 

 manganese dioxide, which Bunzell and Hasselbring (1917) found in solu- 

 tion after decomposition of potassium permanganate, would not be present. 



Kelley (1912), in his work on the manganiferous soils of Hawaii, found 

 a peculiar effect on the roots of plants growing in these soils. In most 

 cases in which the manganese was not present in highly toxic concentra- 

 tions, the roots were found to be highly developed, as appears from the 

 following statement (Kelley, 1912; 34): "Certain other plants, as for 

 instance barley, wheat, oats, and jack beans were found to develop an 

 unusual number of fine rootlets. In the case of barley this was especially 

 noticeable." As stated earlier in the bulletin cited (page 26 of reference), 

 " the root development [of corn] was found to be more extensive than in 

 the normal soil," tho the top growth was retarded. 



Lipman (1913), in determining the effects of salts of copper, zinc, and 

 manganese on the growth of wheat and vetch in soil cultures, found that 

 manganese gave the most marked stimulation, resulting in an increase 

 in dry weight of both tops and roots. 



Howard (1915b) found increased callusing of twigs of Fraxinus when 

 these were coated with a paste of manganese dioxide. He explains this, 

 however, as due to a heat effect resulting from the absorption of Ught. 

 As the stems in the experiments here reported were not exposed to light, 

 no such explanation is possible. 



The stimulation by manganese sulfate may have been due to the man- 

 ganese sulfate as such, or possibly to manganese dioxide deposited on or 

 in the stem as a result of a reaction with the organic matter. The roots 

 of plants grown in a solution containing manganese sulfate showed a 

 browning, apparently due to the precipitation of manganese dioxide. 

 Deatrick, in an investigation at this university, as yet unpublished, also ' 

 found a brown precipitate of the oxide of manganese on the roots of 

 wheat seedlings grown in a solution containing manganese sulfate. The 

 sulfate ion, as well as the manganese, may have played some role in the 

 stimulation by manganese sulfate. 



