Rooting 21 1 



The use of leaves as propagating material requires the differen- 

 tiation of both root and bud primordia. The application of auxins 

 to leaf cuttings may be expected to improve root formation but to 

 hinder bud formation for the reasons described in chapter V. This 

 drawback to the use of auxins on leaf cuttings of Saintpaulia (Warner 

 and Went, 1939) has been alleviated experimentally by the simulta- 

 neous application of adenine to encourage bud formation (Smith and 

 Leopold, unpublished). 



Stolons and roots are sometimes used as propagating material, but 

 they have the limitation that buds are not present and the application 

 of auxin certainly will not help overcome this limitation. The ap- 

 plication of auxin has been found to hinder rather than improve 

 propagation by stolon or root cuttings (Lindner, 1939). This seems 

 reasonable since a low ratio of auxin to adenine is needed for bud 

 formation, and the application of auxin will instead tend to increase 

 the ratio. Very low concentrations of auxin have been found to im- 

 prove rooting of root material provided that large pieces of stolon or 

 root are used (Marth and Hammer, 1943; Warmke and Warmke, 

 1950). 



FACTORS IN SUCCESS 



Environmental Factors 



The ability of cuttings to root in response to auxin applications 

 is influenced by several environmental factors: the season of the year, 

 the photoperiod exposure, and light, temperature, aeration and humid- 

 ity conditions. 



The season at which cuttings are taken greatly affects the ability 

 of the cutting to take root, and the optimum season for taking cut- 

 tings varies immensely between species (Hitchcock and Zimmerman, 

 1930; Brandon, 1939). The succulent new growth appearing on fruit 

 trees in June is favorable material for rooting although other woody 

 plants generally are more easily propagated in the late summer or 

 winter months. Many woody plants are easiest to root if cut in the 

 winter before the buds are ready to break, for at this time the cutting 

 may form callus and differentiate roots over a fairly long period during 

 which there is no foliage to draw on the water supply. 



The photoperiods experienced by the stock plant, or by the cut- 

 ting after placement in the rooting bed, have a distinct effect on 

 rooting. The photoperiods most favorable for rooting vary from plant 

 to plant, with some species rooting best under long and some under 

 short photoperiods (Stoutemyer and Close, 1946; Moskov and Kos- 



