General Physiology of Plants 



187 



of indole acetic acid added to a basic nutrient will 

 give quantitative results which may be expressed 

 in a fairly uniform curve (Fig. 52) (Fiedler, 1936, 

 45; Geiger-Huber, 1936, 214; Geiger-Huber u. 

 Burlet, 1936, 215; Duhamet, 1939, 209; Bonner 



10" l2 to-' 4 



GRAMS- INDOLE-ACETlC-ACID PER ML NUTRIENT 



Fig. 52. Graph showing the relative rates of increment of ex- 

 cised tomato roots grown for one week in a complete nutrient to 

 which had been added (from left to right) decreasing concentrations 

 of indole acetic acid. While 10' 12 and 10" 1S g. of indole acetic acid 

 per ml. of nutrient gave results which might indicate a stimulative 

 effect, the improvement over the control without indole acetic acid 

 was less than the probable error of the experiment and hence of 

 doubtful significance. 



