192 Auxins in Agriculture 



and into the cells of the leaf, and there is no means of accurately con- 

 trolling how much auxin is finally able to enter the plant. Further- 

 more, it is difficult to measure the residue that is left on the surface 

 of the leaf, except in a small carefully controlled application. 



A more quantitatively accurate method of application is by infil- 

 tration of the auxin solutions into the leaves. Some means of infiltrating 

 solutions into leaves include forced infiltration by a sudden increase 

 in pressure (e.g. Claes, 1952), or alternatively gradual infiltration 

 through the cut ends of leaves (Leopold and Thimann, 1949) or 

 through leaves submerged in the solutions (Bonner and Thurlow, 

 1949). Forced infiltration can be done easily by placing the plants in 

 a bell-jar or desiccator with leaves in contact with the solution to be 

 infiltrated. The chamber is evacuated by suction, and then the suction 

 suddenly released. Each of these techniques permits the application 

 of auxin solutions in such a manner that the total amount of solu- 

 tion which has been taken in by the leaf can be measured quanti- 

 tatively. These techniques, of course, do not lend themselves to large- 

 scale or field type of experiments. 



Another means of auxin application is through injection of 

 solutions into fleshy parts of the plant. This can be done either with 

 a hypodermic needle (Galston, 1947), or by a vial with the end 

 drawn out into a capillary which is inserted into the plant at the 

 position to be treated as in figure 54, p. 121 (Zimmerman and Wilco- 

 xon, 1935). Another method is the insertion of one end of a wick into 

 the plant, and the other end into a reservoir of auxin solution. These 

 injection techniques are again fairly good quantitatively and have an 

 additional advantage in that the auxins can be applied to rather 

 restricted plant parts where localization of the application is of 

 interest. 



Simple immersion of the plant part directly into the auxin solu- 

 tion has been done in many instances. Intact leaves, seeds or cuttings 

 from plants have been successfully treated in this manner. The im- 

 mersion of roots in auxin solutions over extended periods of time has 

 been used as a method of studying quantitative effects of various 

 auxins on seedling growth. Burstrom (1950) has found that wheat 

 roots can gradually adapt themselves to grow successfully in solutions 

 of aliphatic acids which initially may be toxic. It is interesting to note 

 that the response of roots or seedlings to immersion in auxin solu- 

 tions may be quite different during the time of immersion than after 

 such immersion treatment has ended. This was first noticed by Thi- 

 mann and Lane (1938), who found that auxin concentrations which 

 inhibited the growth of oat roots immersed in them showed a subse- 



