208 Auxins In Agriculture 



lished by Avery and Johnson (1947), Thimann and Behnke-Rogers 

 (1951), and Audus (1953). 



Techniques of Application 



The three commonest methods ot application ot auxins in the 

 rooting of cuttings are the soak treatment, the dip treatment, and the 

 talc treatment. In the first of these, cuttings are generally soaked for 

 twenty-four hours in auxin concentrations varying from 25 to 100 

 mg./l. The dip treatment is essentially the same except that the time 

 of exposure to the solution ranges from only a few seconds to a few 

 minutes and the effective concentrations are much higher (1000 to 

 10,000 mg./l.). Because of the concentrations used, simple aqueous 

 solutions often do not permit enough solubility and cosolvents are 

 needed. The most common cosolvent is alcohol, and in concentrations 

 as high as 50 per cent (Hitchcock and Zimmerman, 1939). The third 

 common type of treatment involves the use of the dipping of the 

 wet cutting into a talc containing the auxin (Stoutemyer, 1938) in 

 concentrations ranging from 500 to 12,000 mg./l. This method is the 

 simplest one for small operations, but in commercial practice it has 

 the drawback of being less uniform when bundles of cuttings are 

 used. Cuttings on the inside of a bundle are liable to receive insuffi- 

 cient coverage. 



Stoutemyer and O'Rourke (1945) have reported good success with 

 a pretreatment of the stock plant before the cuttings are made. Spray- 

 ing the auxin onto the foliage a few days or a few weeks before the 

 cuttings were made increased rooting ability of a dozen different plant 

 species. This technique is both simple and effective. 



If one treatment of auxin is not quite sufficient, retreatment of 

 the cuttings can sometimes be used successfully (Cooper and Went, 

 1938). 



In most cases where auxins are to be used in the rooting of cut- 

 tings it is not possible to find dependable reports of comparable pre- 

 vious experiments to aid one in determining what auxin concentration 

 to use. For this reason, some preliminary experiments are desirable 

 using a range of auxin concentrations. The first signs of injury due 

 to excessive auxin concentrations are browning of the base of the 

 cutting and inhibition of normal bud development and growth. Once 

 one has determined the concentration at which these undesirable 

 symptoms appear he can proceed with safety by using a lower and 

 more beneficial concentration. 



A method of causing root formation by utilizing the endogenous 

 auxin in the plant instead of applied auxins has been common prac- 



