ALBERT C. HILDEBRANDT 397 



The growth-regulating substances tested included cysteine hydro- 

 chloride, indoIe-3-acetic acid, indolebutyric acid, /7-chlorophenoxyacetic 

 acid, a-naphthaleneacetic acid, a-naphthaleneacetamide, /3-naphthoxy- 

 acetic acid, 2,4-dichlorophenoxyacetic acid, sodium 2,4-dichlorophenoxy- 

 acetate, and 2,4-dichlorophenoxybutyric acid. Each of the compounds, 

 respectively, was added to the basal media in concentrations from 

 I X io~\ I X io~^ ... I X io~^^ grams per liter except indoIe-3-acetic 

 acid which was not tested at i x io~^ grams per liter. Controls without 

 added growth-regulating substance were used. 



Four tissue pieces were incubated in each 125 ml. Erlenmeyer flask. 

 Each concentration was "replicated" six or more times so that twenty- 

 four or more tissue pieces were cultured on each concentration in each 

 trial. In addition certain compounds were tested in trials made at 

 different times of the year. The influence of the growth-regulating 

 substance on growth was measured after six weeks incubation by remov- 

 ing each piece from the flask and by weighing it. 



The average wet weights of cultures incubated on the varying concen- 

 trations of some growth-regulating substances are indicated in Figure i. 

 Only a few curves for some representative growth-regulating substances 

 are presented to conserve space. The weights of the cultures on each of 

 the materials tested were presented elsewhere (11). Statistical analyses 

 of variance showed these differences between concentrations with any 

 one compound to be highly significant. 



With sunflower tissue the differences in weights varied with the con- 

 centration and with the types of growth-regulating substance. Inhibition 

 of sunflower tissue occurred at extremely high dilutions of 2,4-dichloro- 

 phenoxyacetic acid, sodium 2,4-dichlorophenoxyacetate, 2,4-dichloro- 

 phenoxybutyric acid, a-naphthaleneacetic acid and of /J-dichlorophen- 

 oxyacetic acid. An increase in wet weight resulted from high dilutions of 

 a-naphthaleneacetic acid and indole-3-acetic acid. Strong to complete 

 inhibition appeared with all supplements as their strength was increased. 

 Some comparisons of the inhibiting concentrations are presented in 

 Table i. 



With tobacco tissue none of the compounds tested resulted in any 

 large increases in wet weights. All resulted in decreased wet weights at 

 the higher concentrations. The comparative inhibiting concentrations 

 are indicated in Table i. 



The dry weights of sunflower tissue cultures incubated on media 



