THIMANN, BONNER, AND CHRISTIANSEN 



99 



100 



80 



r^vL 



^lOD ADDED 



HOURS 



24 



52 



Figure 2. Protection against iodoacetate inhibition. Sections cut from 64 

 hour coleoptiles, in solutions containing indoleacetic acid i mg. per liter 

 plus sucrose i per cent. Iodoacetate was added 7 hours after placing the 

 sections in solutions; this accounts for the incompleteness of the inhibition 

 at 7 X io~'^M. (10), 



growth studies. The results (Table i) show that the above expectation is 

 reahzed. It is of interest to recall that Sweeney and Thimann (9) some 

 years ago deduced from the study of protoplasmic streaming that the 

 content of organic acids in the coleoptile must decrease with increasing 

 age. 



Pea stem sections, at the age used for our growth tests, have a content 

 of malate and citrate equal to that of very young coleoptiles. This cor- 

 responds well with their relative insensitivity to iodoacetate, of which a 



