Stimulation of Root Growth in Cuttings 133 



results found in the present work, it would seem more probable that the 

 organic matter is acted upon by microorganisms, which results in a 

 decrease in the oxygen supply, an increase in carbon dioxide, and the 

 production of toxic or inhibiting by-products. Each factor enhances 

 the inhibiting effect of the others, and the cuttings are thereby killed or 

 weakened and are then attacked by the fungi. 



It has been shown further that the presence of nutrients has a detrimen- 

 tal effect on woody cuttings, and that an increase in concentration of 

 a nutrient solution distinctly reduces growth. This offers another sug- 

 gestion as to the value of sand as a medium for staa-ting cuttings. Such 

 a medium has, as a rule, less soluble nutrients, is better aerated, and is 

 less likely to contain easily decomposed organic matter, than ordinary soil. 



SUMMARY 



1. The experiments conducted during the course of the present investi- 

 gation show that treatments with potassium permanganate may result 

 in a very marked increase in root growth of various woody cuttings. 

 Five possible explanations for this stimulation have suggested themselves 

 to the author. These are: (1) that the treatment causes a change in 

 the nature of the food supply of the twig; (2) that it affects the rest 

 period of the cuttings, serving to start growth earlier and thereby causing 

 an apparent stimulation of root growth; (3) that it upsets the balance 

 of food supply between the tops and the roots in favor of the latter; (4) that 

 it retards or inhibits growth of microorganisms; (5) that it increases 

 respiratory activity by catalytically hastening oxidation. The results 

 obtained show that the last of these is the most probable explanation. 

 The others may in some cases be of importance in explaining the rooting 

 of cuttings, but the stimulation by potassium permanganate cannot 

 be fully explained in such ways. 



2. Root growth is largely independent of the rest period, for it appears 

 that only the buds, not the whole stem, assume the resting condition. 



3. Manganese dioxide, manganese sulfate, aluminium chloride, ferric 

 chloride, ferric sulfate, boric acid, and possibly phosphoric acid, may at 

 times show a shght stimulating effect on the rooting of cuttings. 



4. Nutrient solutions are, as a rule, injurious to root growth in 

 cuttings. 



