240 



CHEMICAL AGENTS AND GROWTH 



such as the oat coleoptile test as modified by Nitsch and Nitsch 

 (1956), then we obtain the results of Fig. 11. The pattern detected 

 previously with the first internode test holds true here, since the level 

 of auxins is found to decrease sharply after 2 weeks of short days and 



0.0 02 04 06 08 10 00 2 04 06 OS 10 



I I > I I I I I 1 I I I I I < I I I I I I I I 



2 WEEKS SHORT DAYS 



2.0 



I I 

 I I 

 I I 



^[Pi 



I 



Fig. 11. Histograms similar to those of Fig. 10 except that coleoptiles 

 were used instead of first internodes. Left, controls. Right, plants treated 

 with about 10 /».g of GA (from Nitsch 1957b). 



to increase after the treatment with gibberellic acid. In addition, how- 

 ever, one can see on the left side of Fig. 1 1 that under short days a 

 growth-inhibitory zone increases in size and intensity between Rf's 4.0 

 and 9.0. Indeed, after 2 weeks of short days, the sumac tips contain 

 more inhibiting than stimulating substances. 



