Stimulation of Root Growth in Cuttings 131 



reasons put forward to explain this practice is that at that time of the 

 year the sap is flowing downward and would therefore more readily form 

 roots. The commonest reason given is that the cuttings will root better 

 if a callus is allowed to form during the late autumn or early winter, 

 while if no callus is formed the cutting will not root, or at least will not 

 root so readily. 



It would seem, from the results obtained in the present investigation, 

 that this difference in rooting ability between twigs taken in the fall 

 and in the spring is dependent on factors affecting the rest period of the 

 buds, and therefore, indirectly, the food and water supply. Faivre 

 (1871) has pointed out the fact that if woody cuttings are taken in autumn 

 the tops will remain dormant, allowing the roots to form, while if the 

 cuttings are taken in spring the tops will start and use up the stored food 

 which would otherwise be available for root formation. This seems to 

 be the most probable explanation, for, as stated earlier, as a rule the rooting 

 process is slower than the growth of shoots, when the buds are not in 

 the resting condition; the latter therefore develop more rapidly than do 

 the roots, and, as sufficient water for the increased transpiration is not 

 supplied, the shoots wither, causing the whole twig to wither at the same 

 time. The increased top growth also reduces the amount of food available 

 for root formation, as stated above. 



Evidently it is not necessary to callus the cuttings before setting them 

 out if they are taken before they have passed the resting stage. Some 

 workers, however, say that the woody forms, which will not be winter- 

 killed, will strike root just as well if left on the parent plant until spring. 

 On the other hand, as the root development and the callus formation are 

 apparently independent of the rest period, the taking of cuttings when 

 the buds are dormant would allow for a longer period for the com- 

 paratively slow-growing roots and callus to start development, and thus 

 insure a better root growth. If cuttings are taken in the fall and stored 

 at low temperatures, they may have no apparent root development when 

 set out in the spring and yet it is probable that incipient growth has 

 begun. 



Tho stimulation by potassium permanganate has been shown to be 

 independent of an effect on the balance between root and top formation, 

 such a balance can be partially controlled by selecting the right season 

 for taking cuttings, as has just been discussed, or by regulating the tem- 



