Plant Qrowth'Suhstances 



auximone (growth-substance) present in stable manure 

 increased with the progressive decomposition of the manure, 

 though here again a very well-rotted manure contained 

 less auximone than did fresh manure. 



Marked effects of dilute extracts and fractions of farmyard 

 manure upon the extent of production of roots (in their 

 normal positions in water-cultures) have been reported in- 

 dependently by Breazeale (1927) and by Niklewski (1931, 



1935)- 



Breazeale used several dialyzed fractions of manure on wheat 



seedlings and concluded that the effect of the manure extract 



seemed to depend largely on the presence of black organic 



matter, and not upon the amount of plant-food ingredients 



it contained.^ Minute quantities of peat-extract had a very 



striking effect on the growth of citrus seedlings deprived of 



organic matter but well supplied with nitrogen, phosphorus, 



and potash. Niklewski believed that the favourable effect of 



very dilute extracts of manure on the root-development of 



plants was due to colloids, but his earlier work was not 



chemically critical, as he apparently performed no dialysis 



on his manure extracts. 



In a recent publication, Niklewski and Wojciechowski 

 (1937) have brought forward a notable dossier of evidence 

 that minute amounts of manure and peat extracts produce 

 marked effects on the amount of growth of several kinds of 

 plants grown in water, sand, and soil pot, cultures. Plants 

 supplied with the organic extracts and complete mineral 

 nutrients grew much more sturdily than did those supplied 

 with complete minerals only. The extracts were not dialyzed. 

 In the discussion there is, however, but little reference to 

 colloids. 



In a few preliminary field experiments, Niklewski and 

 Wojciechowski attempted to see whether yield effects of 

 normal doses (25 and 50 dz. per hectare) of compost applied as 

 a late top-dressing to cereals had a relation to the water- 

 soluble humus substances in the compost. Increases in yield 



^ Hitchcock and Zimmerman (1935, A) found that three indole acids 

 could pass through a membrane impermeable to the dye Fast Green. 



66 



