HORMONAL REGULATION OF PLANT CELL GROWTH 



203 



constant tliat we simply did not wait long cnongh to detect it. We 

 decided to study this by investigating the effect of changing the 

 rate of metabolism, at one temperature, by using poisons or depriv- 

 ing the cells of Oi>. The speed with which such treatments give 

 effects is likelv to be dependent upon diffusion, but at least an indi- 

 cation of the maximum time required for a change in metabolism to- 

 show itself in the growth rate might be obtained. 







20 



40 



60 

 TIME MIN. 



80 



100 



120 



Fig. 7-2. Effect of transfer from 3 mg per liter indoleacetic acid, at 23° C, 

 to the same plus 3 X 10"^^ M KCN {at first upward-pointing arrow), and back to 

 auxin alone {second arrow). These transfers were repeated at the third and 

 fourth arrows. Coleoptile section 8 mm long, transferred from air to auxin 

 solution at beginning of record. 



Fig. 7-2 shows the effect of changing from auxin to auxin plus 

 3 X 10~^ M KCN, and then after inhibition was complete, back to 

 auxin alone. A fall in the growth rate was detectable 2 minutes 

 after KCN was added, and the half-time for approach to the final 

 inhibited rate was generally about 5 minutes. Upon return to auxin 

 alone, a characteristic lag of 5-10 minutes always occurred, and the 

 rate then quickly returned to, or nearly to, the previously prevailing 



