Growth Regulators in Agriculture 809 



dence that ontogeny repeats phylogeny, because it is suspected that 

 the 'Smooth Cayenne' plant was derived from a spiny ancestor. 



Two points can be made here in respect to Figure 4. One is that 

 the quantitative differences in rate of application of NAA have quali- 

 tatively different effects in differentiation responses. And the second 

 point, which is suggested by this, is that other growth regulators may 

 provide the same desirable over-all effect of inhibition of flowering 

 without some of the undesirable (or at least nonessential) side effects 

 of proliferation of roots, constricted stems, and spininess. We have 

 some evidence that this is so. 



From these illustrations, I should like to derive the principle that 

 a good deal of work remains yet to be done with the substituted aryl- 

 oxyalkyl carboxylic acids and other recognized growth regulators, com- 

 mon or uncommon. Much will be done if horticultural workers will re- 

 fuse to take for granted that all these materials behave the same and 

 vary only in the degree of activity. Admittedly, it is scientifically less 

 satisfying to move into a program of testing without a well-developed 

 hypothesis. We do have some well-developed hypotheses in the test- 

 ing program for crop control in pineapple production, but these were 

 formulated only after empirical testing of several hundred compounds. 

 Some of the earlier hypotheses, as was inevitable, required modifica- 

 tion as the body of test results increased and new evidence became 

 available. However, the net result has been the development of in- 

 formation useful in enlarging our conceptual framework along with 

 its practical value. 



LITERATURE CITED 



1. Clark, H. E., and Kerns, K. R. Control of flowering with phytohormones. 

 Science. 95: 536,537. 1942. 



2. Cowing, D. P. Some experiments on chemical induction of flowering in the 

 pineapple. Plant Physiol. 31 (Suppl.): xxxiv. 1956. 



3. . An antagonism of indolebutyric acid for indoleacetic acid. Plant 



Physiol. 33 (Suppl.): xx. 1958. 



4. Leopold, A. C. Auxins and Plant Growth. 354 pp. Univ. Calif. Press, Berkeley. 

 1955. 



5. Pybus, M. B., Wain, R. L., and Wightman, F. New plant growth-substances with 

 selective herbicidal activity. Nature. 182: 1094, 1095. 1958. 



6. Wain, R. L. Herbicidal selectivity through specific action of plants on com- 

 pounds applied. Jour. Agr. Food Chem. 3: 128-130. 1955. 



DISCUSSION 



Professor Blackman: Since we are discussing tropical applications, 

 perhaps another example might be given where existing knowledge 

 and existing compounds can be used as a basis for a research pro- 

 gram. I am referring to the program on the stimulation of latex flow 



