PROPAGATION OF TREES AND SHRUBS 5 



The making of leaf-bud cuttings, mentioned in connection with a few 

 species, is briefly described in the discussion of Rhododendron, 



Effects of Treatments with Root-Inducing Substances 



Treatment of cuttings with a root-inducing substance such as indole- 

 butyric acid is no substitute for care and skill in handling them; but the 

 effects of treatment, with many although not all species, are to extend the 

 season during which cuttings may be successfully taken (114) and to 

 induce more rapid rooting, rooting in larger percentages, and early de- 

 velopment of more roots per cutting. Cuttings with more roots do not 

 always develop into better plants, however, than those which began with 

 somewhat fewer (117); and if untreated cuttings root in good percentages, 

 the propagator will have to decide for himself whether or not the saving 

 of a few days or weeks in time required for rooting is important enough 

 to warrant treatment (83). But if cuttings rooted by the aid of a root- 

 inducing substance grow no better after rooting than do untreated cut- 

 tings, at least the treated cuttings usually grew no less well (62, 113, 125) 

 and that is a point of some consequence. 



The most common good effect of treatment with a root-inducing sub- 

 stance is to hasten rooting and it is perhaps by this very hastening that 

 rooting is sometimes improved and percentages which root are increased. 

 Cuttings which root more rapidly are, generally speaking, less likely to 

 die unrooted, for the length of life of unrooted cuttings of most species is 

 rather limited. They either root or rot. If they rot, it is partly because 

 they did not root; but if they do not root, it is not necessarily and only 

 because they rot. 



It is unfortunately true that cuttings of species which root with great 

 difficulty or not at all if untreated are the ones least likely to be much 

 benefited and to root well if treated (57), the degree of response being 

 more or less proportional to the ease with which untreated cuttings root 

 (3). But the rooting of cuttings of many species is improved by treatment 

 and as more is learned about the best time to take cuttings, the use and 

 choice of root-inducing substances (there are now some fifty chemical 

 compounds which are known to be growth-promoting (130)), and safe 

 and effective concentrations for each species, the number which it is really 

 difficult to propagate by cuttings will become less. There are at least 

 2550 species of trees and shrubs hardy in North America (84). Ascertain- 

 ing the best treatment and method of handling for all of these or for those 

 which are difficult to propagate by cuttings is slow work but it is proceed- 

 ing and the number of species which can be readily propagated by cut- 

 tings will certainly increase. 



Some Root-Inducing Substances Compared 



Indolebutyric acid, alpha-naphthaleneacetic acid and indoleacetic acid, 

 also their potassium salts (49), are highly effective root-inducing sub- 

 stances; and mixtures of indolebutyric acid and naphthaleneacetic acid 

 are even more effective with cuttings of some species than is either sub- 

 stance alone (50). 



Indolebutyric acid, as used here and by other investigators (12, 43, 48, 

 61, 83, 114), has given better results than indoleacetic acid with cuttings 

 of most species. Among the exceptions are Pyracantha coccinea, Lonicera 



