156 PLANT GROWTH 



In this way horizontal roots accumulate auxin on the lower 

 side, which results in the optimum condition for growth on 

 the upper side. This explains the downward growth of roots. 



Even more interesting is the influence of the synthetic 

 hormones on the rooting of cuttings. The initiation of roots 

 requires stimulation supplied by the growth hormones and a 

 few other chemicals which cause an accumulation of the 

 second hormone, called rhizocauline, at the cut surface from 

 which the new roots start. Roots present on the treated 

 material would be killed by the treatment. Plate X shows 

 the conclusive results of rooting after treatment of holly 

 cuttings. 



Cuttings should be made normally, then placed in the 

 chemical solution (2 to 10 parts in 100,000 parts of water) 

 for 10 to 72 hours. The strength and time should be varied 

 to find the one giving the best results for the particular plants 

 at the particular time of year. A low rate of transpiration 

 from the cuttings gives best results. 



Lanolin paste has been used as a base to carry the rooting 

 hormone, when it can be applied on the cut surface. Rooting 

 compounds can also be purchased mixed with an inert 

 powder, which can be applied to the fresh cuttings, after 

 which it can be placed in the cutting bench at once. 



The values of stimulating the initiation of roots on cut- 

 tings are most important where the untreated ones root with 

 difficulty. Here a higher percentage of cuttings root, and 

 a greater number root in a shorter time. 



Roots, stems, and leaves have been induced to grow roots 

 by this treatment. Hormone action on buds was mentioned 

 in connection with pruning. In most plants the terminal 

 bud secretes the most hormone. It moves downward stimu- 

 lating the elongation of the stem below, but it also inhibits 

 the growth of all lower buds. This has been studied by many 

 people but the details of this growth control are not under- 

 stood. It appears to be an interaction of more than one sub- 



