780 N. E. Tolbert 



Two weeks later the distance in millimeters between the base of the 

 first leaf blade to the base of the second leaf blade was measured, and 

 4 weeks later the total stem height and the weight of the plant were 

 recorded. After some chemical treatments, negative values for the 

 measurement of height were recorded to indicate the distance in 

 millimeters that the base of the second leaf blade lay below the base 

 of the first leaf blade. In these cases the base of the second leaf blade 

 had forced its way out through the sheath of the first leaf blade. 



RESULTS 



Active Structure 



A general structure for the active derivatives is (CH3)3N+CH2- 

 CH2X where X is CI, Br, or the ^CHo group. The chemical names 

 for the three most active compounds are (2-chloroethyl)trimethylam- 

 monium chloride, (2-bromoethyl)trimethylammonium bromide, and 

 (2,3-n-propylene)trimethylammonium bromide. For the growth of 

 wheat and tomatoes these compounds were effective from 10"^ to IO-2 

 M when applied to the soil; from 10-^ to lO-^M when applied as a 

 spray; from 10 " to IQ-^M when applied in nutrient solution to toma- 

 toes; and from less than 10-3 to lO-^M when applied by seed treat- 

 ment. For (2-chloroethyl)trimethylammonium chloride a lO^'Af solu- 

 tion is the same as 0.13 p. p.m. 



A large number of chemicals with related structure were either 

 synthesized or purchased and tested by the wheat bioassay. All com- 

 pounds which were effective on reducing the height of 'Thatcher' 

 wheat plants were also effective in the same proportion when used to 

 treat a variety of other plants. 



From the screening program certain correlations between struc- 

 ture and activity were developed: (a) A trimethylamine at one end of 

 the molecule was essential for activity, (b) The carbon chain which 

 contains the constituent X should be 2 carbons in length for maxi- 

 mum activity. When this chain was 1 carbon long, as in (bromo- 

 methyl)trimethylammonium bromide, the compound Avas less than 

 I/IO as active. When this chain was 3 carbons long, as in (3-bromo- 

 propyl)trimethylammonium bromide, the compound was 1/100 as 

 active, and if this chain were 4 carbons long or branched, the deriva- 

 tive was inactive, (c) The derivatives which were found to be active 

 have had a CI, Br, or ^CHo group substituent for X of the general 

 structure. Other derivatives are still being tested. It is interesting to 

 note that the natural-occurring derivatives, choline, betaine, and 

 phosphorylcholine, were completely inactive. An iodo derivative was 

 toxic. When X was an H, as in (ethyl)trimethylammonium bromide, 

 there was only a trace of activity. 



