PRESIDENTIAL ADDRESS. 73 



of the nutrients bound up with it. The by-products of 

 the bacterial decomposition are many, and have various 

 chemical and physiological activities. Acids there are 

 undoubtedly, and these will attack the mineral fragments, 

 liberating available mineral nutrients. But there are other 

 substances, some of which are injurious to the bacteria 

 themselves, to other micro-organisms and to plants, while 

 some are beneficial and act as accelerators. A better 

 name for what we have previously called toxins might be 

 retarders, while the accelerators have been named auxetics 

 and auximones. 



Schreiner and his colleagues 1 have isolated from soils a 

 number of definite chemical bodies, some of which are 

 injurious, while others are beneficial to plants. In certain 

 unproductive soils the injurious compounds predominate. 

 They are all derived from the organic matter of the soil by 

 the agency of bacteria, and include arginine, guanine, dihy- 

 droxystearic acid, coumarin and aldehydes, such as vanillin 

 and benzoic aldehyde. The toxicity of some of these are 

 overcome by certain fertilising substances, for example, 

 the objectionable activity of vanillin is annulled by nitrates, 

 coumarin by phosphates, and that of p-benzoquinone by 

 potassium salts. 3 



Auximones. 

 Recently Bothamley 3 has discovered that, when peat is 

 fermented with certain aerobic, ammonia-producing soil 

 bacteria, the liquid contains substances which stimulate 

 plant growth. They are related to the vitamines of Funk, 

 but appear to be more closely allied to the growth-produc- 

 ing bodies of Hopkins, which, in exceedingly small amount, 

 are necessary for the growth and well-being of animals. 



1 Through Journ. Chem. Soc, 1914, i, 1195. 



8 Chem. Soc. Rept., 1913. 



3 Proc. Eoy. Soc, B 602, (88) 237. 



