The Study of Growth Substances in Plant Metabolism 



R. H. BURRIS 



TO A group such as this the title Usted on the program, statement of 

 the problem, must appear superfluous. I think this is particularly 

 true in view of the fact that Dr. Thimann's paper constitutes a superb 

 statement of the problem in addition to an answer to certain phases of it. 

 Perhaps it would be more accurate to say that we would now present a 

 restatement of the problem. 



Our concern today is to describe in biochemical terms the mode of 

 action of plant growth substances. It is immediately apparent that this 

 is a big order and one which, in our present state of knowledge, we can 

 complete in a sketchy manner at best. However, an integration of 

 current information and a projection of this into working hypotheses 

 may be useful in directing subsequent efforts. 



In dealing with plant growth substances we must first conscientiously 

 define the particular effect in which we are interested and then employ 

 caution when we translate results obtained there to explain effects of 

 a different nature. This shifting is analogous to shifting from lane to lane 

 in traffic, unless you signal your intentions to others you are likely to 

 be bumped ignominiously in the rear. 



The need for caution in definition of effects and transfer of information 

 from one effect to another arises from the multiplicity of actions of plant 

 growth substances. Not only will a given substance cause different actions 

 on various tissues but even more intriguing is the fact that a variation 

 in the concentration of a growth substance not only will cause a quanti- 

 tative variation in the intensity of a plant response but also may cause a 

 quahtative change in the response. This property is not confined to 

 plant growth substances, for many inhibitors, for example cyanide, may 

 exert a stimulation at very low concentrations. However, the variety 



