Some Accessory Factors in Plant Growth and Nutrition. 241 



several hours. One portion was allowed to dry slowly at room temperature, 

 an alcoholic extract taken and evaporated in vacuo as before, the residue being 

 made up in aqueous solution to a concentration of 10 grm. of carbonated peat 

 per litre. The other portion was leached with water until the washings were 

 colourless, the liquid filtered, and the aqueous extract thus obtained was 

 evaporated in vacuo to dryness. The residue was extracted with alcohol, and 

 the alcoholic solution again evaporated to dryness in vacuo, the residue being 

 taken up with water, filtered, and the clear filtrate diluted to the proportion 

 of the extract of 10 grm. of the original peat per litre. The effect of both 

 these extracts was tested on Azotobacter, three series of cultures being 

 incubated — one containing complete food in distilled water, the second 

 complete food in alcoholic extract of carbonated peat, and the third complete 

 food in alcoholic extract of water-soluble substances from carbonated peat. 

 Again no appreciable effect was observed on the growth of the cultures, while 

 the results of the analyses as given below failed to reveal any stimulation of 

 the organism : — 



Table III. 



Series. 





Nitrogen 



content. 



Nitrogen 

 fixation. 



Mean nitrogen 

 fixation. 









mgrm. 





mgrm. 



mgrm. 





1. 



Control 







•4| 



Mean, 







2. 









•5 JO 



•5 mgrm. 









3. 



Culture 



4 



•8 





4-3 







4. 

 5. 





4 

 4 





 •4 





3-5 

 3-9 



4-0 





6. 





4 



8 





4-3 





II. Complete food + alcoholic 



1. 



Control 



2 



■2-1 



Mean, 







extract of carbonated 



2. 





2 



■2 J 2 



•2 mgrm. 







peat 



3. 



Culture 



4 



•6 



2-4 







4. 





5 



•0 





2-8 







5. 





4 



•4 





2-2 



2-4 





6. 





4 



6 





2 -4 





III. Complete food + alcoholic 



1. 



Control 



1 





Mean, 







extract of water-soluble 



2. 





1 



?b 



'8 mgrm. 







substances from carbon- 



3. 



Culture 



4 



•4 



2-6 





ated peat 



4. 





4 



•2 





2-4 



2-7 





5. 





4 



•6 





2 -8 







6. 





5 



■o 





3'2 





The results thus far obtained tend to prove that the active stimulant of 

 plant growth which is present in bacterised peat does not exist as such in the 

 raw peat, nor can it be liberated by a chemical production of soluble humates. 

 It has been obtained only as a result of bacterial action. 



Cooper and Funk* in 1911 showed that their curative substance was 



* Cooper and Funk, ' Lancet,' p. 1267 (1911). 



