Broader Concepts 7 



and enter into the translocation streams becomes a major consider- 

 ation. The very fact that so many vital processes of the living plant 

 are concentrated in the apical meristem, the phloem parenchyma, and 

 the root system which are relatively well protected from direct ex- 

 posure to chemicals applied to plant surfaces is warning enough that 

 this factor must be considered. There is very substantial evidence 

 that the effective plant regulants do move readily in plant tissues and 

 very often in the general direction of food translocation. 



To this extent they resemble the viruses that move strongly toward 

 and into the roots of perennials in late summer or fall and upward 

 into the growing shoots and expanding buds in the spring. The gen- 

 eral rule for viruses, such as in the yellows disease of beets, is that 

 they move from the areas of ample food reserves to deficient areas 

 where assimilation into tissues is proceeding most rapidly. It has 

 been shown that translocation of foreign bodies into and through 

 the phloem can be accelerated along with sugar by addition of boron. 

 The changes in chemical reactivity attendant to changes in chemi- 

 cal structure have never been properly assayed because it is not clear 

 what vital processes are changed by growth regulants. The materials 

 are reactive and hence undoubtedly affect many enzyme systems. The 

 great problem in perfecting better herbicides, growth stimulants, and 

 retardants is to find methods of accentuating specific reactivities with- 

 out promoting the indiscriminate reactions that are meaningless to 

 cell regulation but exhaust and detoxify the regulant chemical be- 

 fore it can reach the proper site of activity. 



Probably no area of research in the entire pesticide and plant reg- 

 ulant field is more deficient than this one of the proper site of action 

 for a molecule. There is no easy road to its solution because of the 

 terrifically dynamic processes of the functioning and growing cell. 

 However, the experimental approaches must take one of three direc- 

 tions. The physiologist must do everything possible to measure the 

 quantitative changes in cell activity in various tissues of the plant 

 and to determine the change in biochemical activities to see where 

 metabolic processes are accentuated or blocked. This will lead to 

 many blind or false alleys, but eventually a pathway should be un- 

 covered that has real fundamental significance. The second approach 

 is to label or otherwise find the means of tracing the molecule of in- 

 terest as it reacts with cell components or is metabolized into degrad- 

 ation products. Already great progress is being made in this direc- 

 tion. It is somewhat like looking for a needle in a haystack to follow 

 the course of a few millions or thousands of millions of molecules 

 through their various activities in the complex medium of the living 

 cell but it must be done by one means or another. 



The third direction is to study the kinetics of the reaction of var- 



