74 R. GREIG-SMITH. 



These plant stimulants or auximones are soluble in water 

 and in alcohol, and are not destroyed when boiled with 

 water for a short time. Like the vitamines, they form 

 insoluble silver and phosphotungstic acid compounds, which 

 enables them to be partially purified. 



Auximones are formed during the formation of humus 

 from organic matter, and occur in fresh and rotted farmyard 

 manure. 1 There is a greater amount in the rotted than in 

 the fresh manure. They have also been found in the nodules 

 upon the roots of leguminous plants. They are apparently 

 developed, along with certain vitamines, during the germin- 

 ation of seeds. Bothamley claims to have obtained mar- 

 vellous results with the auximones, so much so that they 

 appear to pertain to the nature of the nutrient written 

 about by Wells in " The Food of the Gods." Under the name 

 of "Humogen," a preparation of the auximones is about to 

 be placed upon the market for agricultural and horticultural 

 purposes. 



Toxins. 



Certain plants, and probably this applies to all plants, 

 appear either to secrete or cause the formation of toxins 

 which are injurious, not only to other plants, but even to 

 the plants themselves. A direct secretion of toxin is 

 possible, but an indirect action through a secretion influ- 

 encing the activity of certain groups of soil micro-organisms 

 is probable. A possible direct action has been instanced 

 by Fletcher in the case of maize and Sesamum indicum 

 growing in alternate rows. The latter were injured by the 

 maize, and Fletcher considered that the toxicity may have 

 been due to the secretion of dihydroxystearic acid by the 

 maize roots. 



The indirect formation of toxins is probably seen in the 

 case of soil sickness, which we have reason to believe is 

 due to the activity of certain micro-organisms. 



1 Through Journ. Soc. Chem. Ind., 34, 881. 



