Role of CouDKiriits i)i Growth and Germination 749 



77. Tarragan, M. The efTect of coumarin on the growth of tomato roots in cul 

 tures. Bui. Res. Counc. Israel. 3: 254,255. 1953. 



78. Thimann, K. V., and Bonner, W. D., Jr. Inhibition of plant growth by pro- 

 toanemonin and coumarin, and its prevention by BAL. Proc. Nat. Acad. Sci. 

 U. S. 35: 272-276. 1919. 



79. ^ and Bonner, W. D., Jr. Experiments on the growth and inhibition of 



isolated plant parts. II. The action of several enzyme inhibitors on the growth 

 of the Avena coleoptile and on Pisiim internodes. Amer. Jour. Bot. 36: 214- 

 221. 1949. 



80. Wawzonek, S. Coumarins. pp. 173-216. In: Elderfield, R. C. (ed.) , Hetero- 

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DISCUSSION 



Dr. Wain: In the segment test experiments wliere coumarin was 

 acting as an auxin, so to speak, is it possible that the coumarin ring 

 was opened and ortho-hydroxy cinnamic acid formed? Since cinnamic 

 acid itself is a growth substance, was the ortho-derivative tested for 



these effects? 



Dr. Mayer: No, I don't think ring opening occurs. If you study 

 all the derivatives, coumarin is far the most active. An additional 

 point is that the 3-hydroxy and the 4-hydroxy are both very strong 

 antagonists of coumarin stimulation in growth. It is a very interest- 

 ing point that both the 3- and the 4-hydroxy coumarins, which are 

 rather different in their chemical behavior, are antagonizing growth 

 stimvdation. 



Dr. Burstrom: Your conclusion that coumarin may act as a growth 

 promoter is very interesting, and I recall a paper by Dr. Thimann 

 showing growth promotion by coumarin. I don't remember all of 

 the material, but perhaps Dr. Thimann does. We experimented with 

 several coumarin derivatives years ago, and found a most considerable 

 root growth promotion by daphnetin. It increased root elongation by 

 about 50 per cent, but we didn't follow this up. It may be of interest 

 in connection with your results. 



Dr. Thimann: Yes, we did publish some work on coumarin. It 

 was rather different from what Dr. Mayer has described in that our 

 work was done with sections in the presence of auxin. What hap- 

 pened here was that in low concentrations, and over a fairly wide 

 range, coumarin promoted growth very strongly. At levels of about 

 10-3 jVf it inhibited equally strongly (78). 



The inhibiting part of the curve was log-linear and below that, 

 from 10-« to 10-^ M was the wide range of growth promotion. At the 

 time we reported this we also studied a smaller, but less stable mole- 

 cule, proto-anemonine. It gave exactly the same results but much more 

 powerfully. I do not think this is an auxin effect since it was ob- 

 served in the presence of auxin. 



