481 



Some Effects of Organic Growth- Promoting Substances (Auxi- 

 mones) on the Growth of Lemna minor in Mineral Culture 

 Solutions. 



By W. B. Bottomley, M.A., Professor of Botany, University of London, 



King's College. 



(Communicated by F. W. Oliver, F.B.S. Beceived January 2, 1917.) 

 [Plates 21 and 22.] 



\$£Joe Libretti 



Introduction. 



In a previous communication* experiments were described whicb indicated 

 that when peat is incubated with a mixed culture of aerobic soil organisms 

 for about fourteen days at a temperature of 26° C, a rapid decomposition of 

 the organic matter takes place, with the formation in the " bacterised " peat 

 of certain organic growth-promoting substances or " auximones,"f the addition 

 of which in very small amounts to wheat seedlings growing in water culture 

 causes a marked increase in growth. It was desirable to repeat these 

 experiments with plants in which any variation in growth could be readily 

 and more accurately estimated than in wheat seedlings. 



There was a difficulty at first in selecting a suitable plant for experiment. 

 The objections to using the seedlings of land plants are : the difficulty of 

 accurate weighings at regular intervals ; the fact that a water culture 

 solution is not the natural habitat for a land plant ; the possibility that 

 such seedlings may contain a supply of organic growth-promoting substances 

 produced from the endosperm during germination. Water plants, on the 

 other hand, are usually considered unsuitable for water culture experiments 

 because they will not grow for any length of time in pure mineral culture 

 solutions. Darwin and ActonJ state that " water plants cannot generally be 

 recommended for accurate experiments extending over any considerable 

 time, as we have found it much more difficult to grow them satisfactorily 

 in culture solutions than to grow ordinary plants with the roots immersed." 

 They say, however, " we have found Lemna minor useful for purposes of 



* 1 Roy. Soc. Proc.,' B, vol. 88, pp. 237-247 (1914). 



t In a previous communication ('Roy. Soc. Proc.,' B, vol. 89, p. 102 (1915)) the term 

 " auximone " (Gr. m/£i/ior : promoting growth) has been suggested for these substances. 

 This term may usefully serve as a general descriptive name for these organic plant 

 growth-promoting substances until our knowledge of their true nature and composition 

 is sufficiently extended to warrant the application of a more satisfactory name. 



% Darwin and Acton, 'Practical Physiology of Plants,' pp. 61-63 (1901). 



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