Growth Regulators in Agriculture 



805 



0.3 0.6 1.2 3 6 12 6U bu j^^ 



Level (mg/plant) inducing 50% or more flowering active 



Fig. 1. Lack of correlation between activity in the split pea-stem curvattire test 

 and induction of flowering in the pineapple. Data for 92 substituted phenoxyalkyl 

 carboxylic acids, omitting data for 53 others inactive in the pea test which were 

 also inactive in flower induction. 



The emphasis in the previous paragraphs was on toxicity, but the 

 point should be recognized that there are qualitative differences in 

 morphogenic responses between compounds which assay as "auxin 

 in common in growth responses. 



From Figure 1 it can be readily seen that there is no particular 

 correlation between activity in the split pea-stem curvature test and 

 ability to induce flowering in the pineapple plant. Of the 92 variously 

 substituted phenoxyalkyl carboxylic acids shown active in the pea test, 

 only 33 were active in flower induction. The compounds inactive in 

 flower induction ranged from 6 to 249 per cent of the activity of NAA 

 in the pea test, and were tested in many cases on pineapple at rates 

 up to a toxic level. 



Another example was reported some time ago by Leopold (4, 

 p. 302) in connection with pineapple. He pointed out that the use of 



