Natural auxins 



Similar investigations concerning the effect of pH and buffer concentration 

 gave the results shown in Figures 15 and 16. Accordingly, a pH of 5-0 was 

 used in all our experiments and a concentration of 10~^ M for KgHPO^ in 

 the buffer was adopted. This is not the optimal concentration as far as the 



i 



^■0- 



3-0 



I 



80 



10 



Ai^ena 

 coleoptile 



0-1 



(b) 



Sorjhum 

 first infernode 



Alpena f/nsf 

 inhnnode 



10 0-1 1 10 0-1 



Buffer concentration ^ fO'^ M 



Figure 16. Effect of concentration of citrate-K phosphate buffer at pH 5-0 in the presence of 

 sucrose on the growth of 4 mm sections. The lAA concentration was 50 yjl. in the case of oat coleoptiles 

 and 10 yjl. for sorghum and oat first internodes. The concentration given along the abscissa is that of the 

 K2HPO4 component; the concentration of citric acid is one half of it. 



coleoptile sections are concerned, but it was feared that lowering the con- 

 centration would diminish the buffering capacity to such an extent that 

 certain compounds separated on the chromatograms of plant extracts would 

 change the pH considerably. 





-^3-0 



E-0 ^ 



1-0 



I 

 ^1-0 







Coleoptile 



First internode 



(a) 



lAASoJl. 



/ 



^ 



(1)) 



Cc) 



IAAiOy/l. 



Con. 



15 18^21 Bf 



39 15 18 ^y 39 



Time Hrs 



Figure 17. Effect o/^length of incubation on growth of oat sections in buffer -\- sucrose without added 

 lAA {white circles, dotted lines) and with lAA {black circles, solid lines), and on the difference between 

 these growths {curves {b) and {d)). Before time 0, the coleoptile sections had been presoaked for 3-5 hours in 

 MnS04 ■ H2O (1 mg\l.) and the internode sections for 1 hour in glass-distilled water. To exclude the 

 effect of light during the measurements, 5 replicates of 10 sections each were started at the same time ; at 

 each time interval, one of these dishes was measured and discarded. 



The relationship between elongation and time of growth in the solution 

 was also investigated. By starting with a certain number of replicate dishes 

 and measuring one of them at various time intervals, the curves o^ Figure 17 



22 



