Role of Coumarins in Groivth and Germination 



739 



indicating specific differences between species in tlieir response. Good- 

 win and Taves, and Mayer and Evenari stress tlie importance of tfie 

 unsaturated lactone linked to an aromatic nucleus. 



The only data available on stimulatory action as related to struc- 

 ture are those of Neumann (51). He found that both 3- and 4-hydroxy- 

 coumarins are growth inhibitors at concentrations at which coumarin 

 itself stimulates (Table 1). 3-Methyl and 3-chIoro substitution reduced 

 stimulatory activity of coumarin considerably, but the substances still 

 had some activity at concentrations at which the hydroxy derivatives 

 were inhibiting. Trans-o-coumaric acid and melilotic acid (dihydro-o- 



Table 1 . 

 growth. * 



The effect of various coumarin derivatives on germination and root 



Derivative ot 

 5 4 



8 







Effect on 



Germination of 



Lettuce Seed 



Parent compound. 



3-Methyl- 



4-Methyl- 



5-Methyl- 



6-Methyl- 



7-Methyl- 



8-Methyl- 



3-Hydroxy- 



4-Hydroxy- 



6-Hydroxy- 



7-Hydroxy- 



3-Chloro- 



6-Chloro- 



Coumarin-3-car- 



boxylic acid. 

 7,8-Dihydroxy- 



7,8-Dihydroxy-4- 

 methyl- 



7-Hydroxy-4- 

 methyl- . . . 



Strong inhibitor 

 Weak inhibitor 



Very weak inhibitor 

 Very weak inhibitor 

 Very weak inhibitor 

 Very weak inhibitor 

 Weak inhibitor 

 Weak inhibitor 



Very weak inhibitor 

 Almost not an 

 inhibitor 



Effect on 



Root Growth 



of Avena 



Strong inhibitor 

 W^eak inhibitor 

 Weak inhibitor 

 Weak inhibitor 

 Weak inhibitor 

 Weak inhibitor 

 Strong inhibitor 

 Very weak inhibitor 



5,7-Dihydroxy- 



6-Methoxy-7- 

 hydroxy- . . . 



Almost not an 

 inhibitor 



Almost not an 

 inhibitor 



Almost not an 

 inhibitor 



Strong inhibitor 

 Strong inhibitor 



Strong inhibitor 



Very weak inhibitor 

 Very weak inhibitor 



Very weak inhibitor 



Effect on 

 Stem Growth 

 of Sunflower 



Stimulator 

 Weak stimulator 



Inhibitor 

 Inhibitor 

 Stimulator 



Weak stimulator 



* The results on germination were taken from Mayer and Evenari (44) : Inhibition 

 index of 1.0 in Mayer and Evenari = strong inhibition. Inhibition index 0.9 to 0.25, 

 weak inhibitor. Inhibition index < 0.25, very weak inhibition. The results of root 

 growth were taken from Goodwin and Taves (16): First group— strong inhibition; 

 second group — weak inhibition; third group — very weak inhibition. The results on 

 stem growth were taken from Neumann (52). 



