Role of Auxins in Control of Leaf Senescence 339 



one is, in fact, getting increased senescence in the sm-rounding tis- 

 sues following a local 2,4-D treatment. 



Dr. Wareing: ^Ve have been doing some experiments which bear 

 on Dr. Osborne's results. We are primarily interested in the possible 

 effect of auxin on translocation, and have been feeding labeled sugar 

 to older leaves of bean plants in the basal region of the plant and 

 tracing the movement of the sugar without any applied lAA. As many 

 people have found, we got movement from the applied mature leaf 

 toward the young growing leaf. There is no appreciable movement 

 into already mature leaves between the applied leaf and the shoot 

 apex. If lAA is applied to one of these mature leaves, then sucrose 

 moves into that leaf instead of into the young growing leaves. So, 

 here again, ^ve have movement of labeled nutrients toward a region 

 where hormone is applied. 



Dr. Crafts: We have found, using labeled urea, that we get an ex- 

 tremely rapid splitting of the urea and synthesis of the labeled car- 

 bon dioxide into sugar. The sugar moved in a perfectly normal fash- 

 ion, indicating that this labeled urea may be a much handier tool 

 than the sugar — cheaper, much more readily absorbed by the plant, 

 and apparently perfectly normal in its distribution. 



Dr. Bach: A minor technical point: Are you sure that the labeling 

 you observed after the application of radioactive 2,4-D is actually in 

 the tissue, not on top of it, or perhaps dissolved in the waxy layers? 



Dr. Osborne: As Dr. Crafts has just said, perhaps the tissues would 

 not respond unless some of the 2,4-D entered the leaf. The green 

 areas correspond closely to the areas of radioactivity, but I have not 

 extracted the leaves to determine the amount of activity actually 

 within the tissue. 



Dr. Freed: In Dr. Osborne's discussion here I was reminded of a 

 famous name in auxinology, that of Dr. Ezra J. Kraus. He retired to 

 Corvallis, Oregon, and shortly after his retirement suggested an ex- 

 periment which consisted of treating a plant with lAA and 2,4-D and 

 then measuring the amount of sugar and phosphorus accumulating 

 in the various areas of the leaf. Now this was not with exogenously 

 applied sugar or phosphate but with only the normal metabolic su- 

 gars, etc. Results showed an accumulation in the hypocotyl of both 

 the sugar and phosphate in the plant. Radioautograms and chiomato- 

 graphic studies showed that the 2,4-D accumulated in the bean hypo- 

 cotyl, bearing out Dr. Osborne's findings. 



Dr. Osborne: We have done a few experiments in which we fed 

 the plants labeled phosphate and then put on the 2,4-D spots after- 

 wards, but we found no evidence of an accumulation of phosphate in 



