756 Hall, MilleVj ajid Herrero 



A second series of cotton seedlings with two true leaves were 

 treated in the same manner (2,000 p.p.m. of ethylene-C'^ in the root 

 medium). Plants were harvested for radioautographing 1, 2, 4, and 8 

 hrs. after introducing the ethylene. The intact plants were pressed 

 between blotters and frozen. They were lyophilized while pressed, 

 mounted, and radioautographed against No-screen X-ray film for 

 one month. The radioautograms indicated that ethylene was ab- 

 sorbed rapidly by the roots and translocation of its metabolites oc- 

 curred almost uniformly throughout the plant within the first hr. 

 Maximum activity in the leaves was reached in 2 hrs.; however, after 

 4 hrs. activity decreased in the leaves indicating that the metabolites 

 were being converted to a gaseous form and emitted. The nature of 

 the released radioactive gas is being studied currently by means of the 

 vapor fractometer and vibrating reed electrometer. Tentatively, the gas 

 does not appear to be carbon dioxide. 



Single Leaf Treatments 



Single, detached, fully-expanded cotton leaves were treated in the 

 light (2,000 foot candles) and in the dark (< 1.0 foot candle) in a "lol- 

 lipop" flask. The trials were conducted to determine the feasibility of 

 short-term treatments in a manner similar to those used to study 

 photosynthetic intermediates of carbon dioxide fixation. Considerably 

 less fixation occurred in 3.5 to 5 hrs. in the detached leaf than when 

 the single leaf was attached to the plant during treatment. There was 

 three to five times more ethylene fixed in the dark than in the light, 

 suggesting that photosynthesis is probably not involved directly in 

 ethylene fixation by leaves. 



When the treated leaves were oven-dried overnight at 60° to 

 70° C. about 79 per cent of the fixed radioactivity was lost. This sug- 

 gests that a major portion of the fixed ethylene is in loose combina- 

 tion in the leaf. Therefore, lyophilization was used in most of the 

 subsequent studies. 



Influence of Leaf Age on Ethylene Fixation 



The tops of six cotton plants in the early-fruiting stage were 

 treated with 6.9 ml. of ethylene-C^^ in an eleven-liter chamber. The 

 atmosphere inside the chamber contained about 600 p.p.m. of ethy- 

 lene. Light intensity was reduced to less than one foot candle during 

 the 16 hr. exposure period. Leaves were harvested separately, num- 

 bered from 1 to 6 from the apex to the base, dried, ground, and 

 pressed into uniform briquettes for coiniting. The residts given in 

 Figure 2B show that, in general, the younger the leaf the more ethy- 

 lene it fixed. The number one leaves which were about 2 cm. in 



