210 Auxins in Agriculture 



have sufficient undifferentiated tissues to permit easy differentiation of 

 root primordia and they also have buds already formed. As we have 

 already pointed out, the work of Skoog (1944) indicates that auxin 

 treatments which favor rooting do not promote bud formation; 

 hence it is desirable to have buds already formed on propagation 

 pieces. For these reasons stems are the commonest structures used in 

 vegetative propagation. 



It is interesting to note that woody stems are more susceptible to 

 injury from auxin treatment than herbaceous stems. In fact, suscepti- 

 bility to injury increases with increasing woodiness (Maxon et al, 

 1940). 



In selecting woody stem material for rooting it is interesting to 

 note that cuttings taken from the lower branches of trees quite com- 

 monly root more readily in response to auxin than do cuttings from 

 the tops (Grace, 1939). This has been confirmed in the case of many 

 species, and is probably due to nutritive differences in the stems. 



The age of the wood from which a cutting is made has a real 

 influence on rooting. Succulent new shoots are generally the easiest to 

 root. Practically all experiments with woody plants seem to show 

 consistently that one-year-old wood is the easiest to root. Besides the 

 age of the cutting itself, the age of the stock plant from which the 

 cutting is made also influences rooting capacity. Cuttings from older 

 stock plants appear to be progressively more difficult to root with or 

 without auxin treatment, even when uniform, one-year-old wood is 

 taken for the cutting (Thimann and Delisle, 1942). An interesting 

 observation has been made by Day (1932), that wounding of cuttings 

 quite generally stimulates subsequent rooting capacity. Wounding 

 seems to improve the rooting response to auxins as well (Thimann 

 and Behnke-Rogers, 1950), 



The beneficial effect of leaves has already been mentioned. Leaves 

 themselves are often easily rooted, perhaps because of the abundant 

 supply in the leaves of materials known to stimulate rooting (van 

 Overbeek et al, 1946). The leaves of many plants root without auxin 

 application as, for example, Kalanchoe, Saintpaulia, and Bryophyllum. 

 Leaves of others such as pineapple, tomato, begonia, and Indian 

 rubber will root in response to auxin treatment. Cutting the veins 

 has been found to increase the rooting response of begonia and Indian 

 rubber (Balansard and Pellissier, 1942), perhaps because of accumula- 

 tion of growth substances at several points and consequent rooting 

 there instead of just at the base of the petiole. Lily bulb scales have 

 been used as propagating materials and respond well to auxin treat- 

 ment (Avery and Johnson, 1947). 



