10 G. L. McNew 



wheat crop was reasonably protected only 20 years according to no 

 less authority than Stakman and Harrar (Plant Pathology, Ronald 

 Press, N. Y. 1957, page 507). 



The use of fungicides to meet these recurring crises comes to mind 

 at once, but keeping all the wheat fields covered with a protective 

 fungicide throughout the season is economically unsound. The real 

 need is for a growth regulant that would alter the innate susceptibil- 

 ity of a plant for 30 or even 10 days. Such material could be applied 

 when the need for it was apparent, and only then. If the activity 

 of a single gene will impart immunity to a specific race of rust fungus, 

 is it too much to expect someone to find a chemical with equal resis- 

 tance-regulation capacity? 



Looking toward other outlets for research in plant regulation, we 

 become aware that the quality of plant products could be improved 

 tremendously. For too many years the plant scientist has been overly 

 concerned with quantity of produce rather than its quality. Most bota- 

 nists are fully aware that by use of hybridization the average yield 

 of maize was increased about 90 per cent in the United States within 

 two decades. However, the yield of protein per acre held almost con- 

 stant. The achievement was primarily in production of starch. There 

 is no reason why chemical controls should not be available to increase 

 nitrogen assimilation in proteinaceous crops, balancing of sucrose and 

 other sugars with organic acids in fruits, or storage of starch or sugar 

 in root crops. 



There is little need to dwell on these and other areas of potential 

 service to agriculture. Great opportunities lie ahead if we can only 

 develop sound concepts as to how cells function and grow. 



If we are to regulate plant growth in specific directions as indi- 

 cated here, we must have a clear concept of what constitutes plant 

 growth. In the broad sense it is the sum total of all cell activities 

 that lead to normal expansion, differentiation, and multiplication of 

 cells so that they may be incorporated into new, functional tissues 

 and organs. Growth, therefore, starts in the processes of cell division, 

 progresses with cell enlargement, and culminates in cell differentia- 

 tion. 



The course and rapidity of any one of these stages of growth will 

 be determined by the balance existing between cell constituents. 

 These balances are both chemical and physical; for example, hydro- 

 static pressure vs. strength of cell wall, pectic substances vs. lignin 

 deposition, food reserve vs. water supply, etc. It would be unwise to 

 believe that any one chemical that we ordinary mortals might syn- 

 thesize will be all-powerful in determining the course of cell multi- 

 plication, enlargment, or differentiation. The most it can do is to 



