738 A. M. Mayer and A. Poljakoff-Mayber 



marin concentrations (lO-i^ A/). Norman and Weintraub (53) in- 

 cluded coumarin in the list of ciiemicals causing root initiation. Gi- 

 gantism in initial cells of MarcJinntia, caused by coumarin treatment, 

 was reported by Rousseau (70). Buis (7) showed that 10 to 100 p.p.m. 

 of coumarin affected both the size and number of sprouts of maize 

 plants, an effect which may be closely related to the abolition of apical 

 dominance (8). 



Neumann (51, 52, and impublished^) in our laboratory has shown 

 that coumarin can stimulate the growth of a number of plant tissues. 

 He showed that the elongation of sunflower hypocotyls is stimulated 

 by coumarin concentrations of 250 p.p.m. and that inhibitory effects 

 were only noted at 1,000 p.p.m. Similar effects have been sho^vn by 

 Neumann for pea stems, bean hypocotyls, and Avena coleoptiles, al- 

 though in this latter material the effect was less pronounced and lim- 

 ited to a very narrow range of concentrations. This stimulation was 

 similar to that obtained with 1-naphthaleneacetic acid. Thus the 

 stimulatory action of coumarin on the growth of plant tissue is not 

 confined to any one plant tissue but is a more general response. It 

 seems as though coumarin can act as a genuine auxin since, first, in 

 various ranges of concentrations it stimulates elongation of stem tis- 

 sue; secondly, though it generally inhibits growth of roots, in very 

 low concentrations it stimulates the latter; thirdly, it stimulates the 

 expansion of leaf tissue, cambial activity, and root initiation. The re- 

 cent findings of Misra and Patnaik (48) also lend support to such a 

 view. 



The relation between structure and activity of coumarin and its 

 derivatives has been studied in detail only in a few cases. Goodwin and 

 Taves (16) have shown that coumarin is the most powerfid root 

 growth inhibitor but some of its derivatives were almost as active 

 as coumarin itself, namely, 7,8-dihydroxycoumarin, 7,8-dihydroxy-4- 

 methylcoumarin, 8-methylcoumarin, and coimiarin-3-carboxylic acid. 

 3-Methyl substitution greatly diminished the inhibitory action on root 

 growth (Table 1). San Antonio (72), on not very convincing evidence, 

 claimed that the lactone structure is not essential for inhibitory action 

 of coumarin on growth and germination. He tested only few deriva- 

 tives, and these under special conditions. Mayer and Evenari (43) have 

 shown I hat germination inhibition by coumarin is definitely a func- 

 tion of the unsaturated lactone structure. All derivatives of coumarin 

 were less active ihan (oumarin itself. However, it is of special signifi- 

 cance that very ajjpreciable differences were observed by Mayer and 

 Evenari between the ies})onse of wheat and lettuce seed to coumarin, 



^ Added in proof: Ncuinaiiii, J. Tlic iiaiuic of the growth -})ioniuiiiig action ol 

 coumarin. Physiol. Plant. 13: 328-341. lOGO. 



