332 



D. J. Osborne and M. Hallaway 



J 300 



O 



LJ 



? 



I 



cn 



LlJ 

 (T 

 li. 200 



C3 



tr 

 o 



X 



100 



"I r 



"1 r 



T r 



2,4-D treated areos of leaf 



2,4-D untreoled areas of leaf 



Control leoves 



8 



DAYS AFTER TREATMENT 



10 



14 



Fig. 1. Oxygen consumption by leaf discs cut from 2,4-D-treated Euonymus leaves 

 and from control leaves at various time intervals after treatment. Values indi- 

 cated by triangles at I and 3.5 days are for ethanol-treated control leaves. Dupli- 

 cate values are indicated bv vertical lines. 



The nitrogen values given in Figure 2 show that after 3.5 days 

 no measurable changes had occurred in any of the nitrogen fractions; 

 but by the sixth day a significant fall in both total and alcohol- 

 insoluble nitrogen had taken place in the untreated areas of the 

 2,4-D-treated leaves. This coincided with the first visible signs 

 of yellowing in the untreated parts of the blade. At no time 

 was there a net loss of total nitrogen or of protein in the 

 2,4-D-treated areas. The evidence suggests that there is an ac- 

 tual increase in both these fractions and it seemed likely that some 

 of the nitrogen lost by the untreated parts of the leaf might be ac- 

 cumulated within the 2,4-D-treated tissues. This supposition is sup- 

 ported by the fact that yellowing occms first in the tissues immediately 

 surrounding the treated spot; the premature senescence of these sur- 

 rounding tissues might well be due to a migration of readily respir- 

 able substrates from the areas of low auxin concentration towards 

 those of high auxin concentration in which there is a high rate of 

 oxygen consumption. Evidence for the acciunulation of nitrogen 

 compounds and possibly also for carbon comjjoiuuls by the 2,4-D- 

 treatcd tissues was obtained from the following experiments. 



Evidence for the Accumulation of Carbon Compounds 



The leaves of a small branch of an outdoor Euonymus bush were 

 labeled with C^^ in the following way: the branch was enclosed in a 



