212 Auxins in Agriculture 



chezhenko, 1939). Some evidence suggests that the photoperiods most 

 favorable for rooting are those in which carbohydrate reserves are 

 accumulated in the cutting. While there is an interaction with nitro- 

 gen — that is, cuttings high in nitrogen will not show as good a re- 

 sponse to carbohydrate accumulation in terms of rooting — still the 

 photoperiod influence appears to be largely a consequence of its 

 effect on the carbohydrates of the plant (Smith, 1926). The photo- 

 periods experienced by the stock plant before the cuttings are made 

 have a more profound effect on the ability of the cutting to root than 

 the photoperiods experienced by the cutting itself (Pridham, 1942). 



Light itself has an effect on root initiation. If the eirtire piece 

 of plant material is exposed to light, root initiation commonly is 

 inhibited and, furthermore, root growth is inhibited once root ini- 

 tiation has taken place (Went, 1935). On the other hand, if the 

 cutting is embedded in a rooting medium and light is applied only 

 to the parts above ground, a stimulation of rooting is sometimes pro- 

 duced (Stoutemyer and Close, 1946). For this reason, then, the appli- 

 cation of light to leafy cuttings is often found to be beneficial. Stoute- 

 myer and Close have found that red light is more effective in pro- 

 moting rooting than blue light. It is curious to note that red light 

 applied to the stock plant before the cutting is made has likewise 

 been found to stimulate subsequent rooting ability (ibid). 



The temperature atid aeration conditions under which the cut- 

 ting is kept, of course, have a strong influence on the rooting obtained. 

 Low temperatures in general seem to promote the formation of callus 

 tissue and, as one would expect, the development of root primordia on 

 undifferentiated callus tissue is much easier than the formation of 

 roots from well-differentiated tissues. 



The growth of roots is favored by higher temperatures, so many 

 rooting beds are heated from below. In commercial practice cuttings 

 are often stored in cool places to permit callus formation and then are 

 placed in warm rooting beds to facilitate the growth of the roots. 



All known types of auxin stimulation of growth are aerobic in 

 nature and hence it is not sin prising that good aeration is essential 

 to rooting of cuttings. 



High humidities are helpful in rooting cuttings. Obviously the 

 cutting is poorly equipped to obtain water for transpiration, so it is 

 quite susceptible to damage by low humidity. 



Physiological Factors 



Several physiological factors inherent in the cuttings themselves 

 are known to be important in the rooting of cuttings. One of these 



