Stimulation of Root Growth in Cuttings 99 



eral instances in which investigators have found that manganese is im- 

 portant in the action of a number of oxidases. 



It would therefore seem reasonable to explain the marked stimulation 

 obtained with treatment by potassium permanganate as due to the effect 

 of the manganese dioxide, deposited on and in the twig, on the respiratory 

 activity of the cutting, either by directly hastening respiration or by 

 causing more complete oxidation and thereby preventing the accumula- 

 tion of partially oxidized, toxic, or inhibiting products of catabohsm. 

 Such an effect occurring within the tissues would be very similar to that 

 which may occur in the external medium in the presence of microorgan- 

 isms, as discussed later. 



The lack of stimulation with certain forms, notably Salix, may be 

 explained on the theory that the oxygen supply does not become a limiting 

 factor with such forms, and therefore, as the effect of the manganese is 

 merely to increase oxidation, no increased growth is to be expected. The 

 fact that Cannon and Free (1917) found Salix to be peculiar in that its 

 roots were uninjured by lack of oxygen or excess of carbon dioxide, lends 

 weight to this explanation. 



Effect of treatment on growth of microorganisms 



The increased growth of roots when cuttings are treated with potassium 

 permanganate cannot be due to any direct effect in keeping the solution 

 sterile and free from microorganisms, altho in experiments with Pyrus 

 malus, Evonymus europaea, and Forsythia sp., and also in other experi- 

 ments not here reported, the cuttings treated with permanganate remained 

 alive and vigorous for a much longer period without root formation than 

 did the checks. Pyrus twigs remained in good condition for from six to 

 ten months, while most of the check twigs were rotting after from one 

 to three months. On close examination the treated twigs appeared to 

 be heavily coated with a slimy growth of fungi and bacteria, yet they 

 were*aUve and healthy. The cultures were certainly not sterile; in fact, 

 in one experiment several of the cultures that showed the greatest root 

 growth apparently had a growth of microorganisms even greater than 

 that in the cultures not treated with permanganate. As shown in table 7, 

 the twigs in the culture with 0.004 molecular cane sugar were slimy to 

 a slight extent on December 18, and those in the culture with 0.004 

 molecular cane sugar plus . 004 molecular potassium permanganate were 



