210 GROWTH 



malacoides treated with an aqueous extract of 0-i8 gram of 

 bacterized peat grew taller than untreated plants. This 

 aqueous extract contained 20 mg. of organic matter, of which 

 only 1-9 mg. represented nitrogen. 



Bottomley's suggestion that nucleic acid derivatives are 

 responsible for the auximonic action has been further examined 

 by Mockeridge * who found that such bodies occur in many 

 manurial composts and her cultural experiments indicated that 

 the greater the decomposition of such manures, the more effec- 

 tive is a water extract of them in promoting growth. The conclu- 

 sion is therefore reached that the free bases of nucleic acid are 

 more effective than undecomposed nucleic acid. In a further 

 investigation, -j- it was found that the increase in the growth of 

 Lemna minor was approximately proportional to the amount 

 of nucleic acid derivatives added to the culture solution. 



Azotobacler and Bacillus radicicola, nitrogen-fixing organ- 

 isms, were the subjects in this investigation : it was found 

 that sterilized cultures of Azotobacter increased the growth of 

 Lemna, although the increase was not proportional to the 

 amount of Azotobacter added. Autoclaved and autolyzed yeast 

 similarly have growth-promoting powers, the autoclaved being 

 more potent than the autolyzed. Yeast contains nucleic acid 

 radicles and the bacteria mentioned also have the necessary 

 radicles for the formation of nucleic acid. 



Possibly auximones are connected with the synthesis of 

 complex nitrogenous molecules, for their action on the nit- 

 rogen cycle organisms is to increase the rate of nitrogen 

 fixation and nitrification and to depress the rate of denitri- 

 fication. There is no doubt that the use of bacterized peat 

 may give marked positive results in pot cultures, but to what 

 extent the treatment is advantageous to field crops is doubtful.^ 



It must, however, be mentioned that evidence is not wanting 

 to indicate that such auximones are not essential for plant 

 growth, although they may have an accelerating action. § 



* Mockeridge : " Biochem. Journ.," 1920, 14, 432. 

 f Mockeridge : " Ann. Bot.," 1924, 38, 723. 

 X See Russell : " Journ. Board Agric," 1917, 24, 11. 

 § See Clark: "Journ. Ind. Eng. Chem.," 1924, 16, 249; "Plant 

 Physiol.," 1926, 1, 273. Saeger: "Journ. Gen. Physiol.," 1925, 7, 517. 



