662 ]. van Overbeek and L. Dowding 



nothing in the literature that would disagree with such a view — then 

 the well-known inhibition of root elongation by auxins could easily 

 be explained. 



LITERATURE CITED 



1. Kato, J. Studies on the physiological effect of gibberellin II. On the interaction 

 of gibberellin with auxins and growth inhibitors. Physiol. Plant. 11: 10-15. 1958. 



2. van Overbeek, J. Auxins. Bot. Rev. 25: 269-350. 1959. 



3. , Racusen, D. W., Tagami, M., and Hughes, W. J. Simultaneous analysis 



of auxin and gibberellins. Plant Physiol. 32 (suppl.): xxxii. 1957. 



4. Walhood, V. T. The effect of gibberellins on boll retention and tut-out in cot- 

 ton. Proc. 12th Ann. Cotton Conf. Memphis. Dec, 1957. 



5. Wickson, M., and Thimann, K. V. The antagonism of auxin and kinetin in 

 apical dominance. Physiol. Plant. 11: 62-74. 1958. 



DISCUSSION 



Mr. Barlow: We have used a leaf base test similar to that described 

 by Dr. van Overbeek. It was a slight modification of the test pub- 

 lished by Margaret Radley (Ann. Bot., N.S. 22: 297. 1958) in which 

 the wheat leaf base is used instead of the Avena leaf base. We didn't 

 observe this depression of GA stimulation by lAA. I'm wondering if it 

 is partly due to the age of the coleoptile which is used. Radley recom- 

 mended rather old, long, coleoptiles and used a basal 1-cm. section. 

 In that case, of course, the coleoptile section itself doesn't extend, but 

 the leaf grows considerably. I also noticed in yoin^ photographs that 

 the leaf only seemed to grow out of one end of the section. In our 

 experience, the leaf expands on both sides, leaving the coleoptile sec- 

 tion in the middle. Could you tell me if the growth of that leaf is 

 due primarily to enlargement of the cells, or is it due to cell division? 

 I have had a very brief look at this and, as far as I could see, most of 

 the increase in length was due to cell extension. Right at the base of 

 the leaf, however, it became extremely difficidt to say whether, in fact, 

 the cells were growing (in Prof. Thimann's sense of the word growth) 

 or whether in fact the leaf base was adding cells. 



Dr. van Overbeek: I can answer part of those questions. We cut 

 the section below the node; when we cut it above the node, the leaf 

 grows out on both sides. We have found variability at times, and we 

 thought that part of the answer was the age of the seedling. We tried 

 different ages and still found this inhibition. In oat seedlings, age 

 apparently is not the principal lac tor in the inhibition of G.A. stimu- 

 lation by lAA. Whether the elongation was cell division or cell en- 

 largement, I do not know. We do have the complete bud here, and 

 since there is a certain amount of lag in growth response to G\, it is 

 possible, although unlikely, that cell division is involved. I iliink it is 

 growth in the sense of Thimann's elongation. 



