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Ethylene gas in minute quantities plays an important role in plant metabolism, especially in the ripening of fruits. A sensitive quantitative analytical method has long been needed. In the method reported here, ethylene is absorbed from an air stream in a solution of mercuric perchlorate, forming an ethylene-mercury complex. The accumulated ethylene is later released from the complex by the addition of hydrochloric acid, and its volume is measured manometrically. This method THYLENE gas in minute quantities plays an important role E in plant metabolism. It stimulates marked physiological changes, such as an increase in respiratory activity and such chemical transformations of reserve materials as the change of starch to sugar. The hastening of ripening of fruits by use of ethylene gas has been knoRn for many years (4,11). Later it was discovered that naturally ripening fruits themselves produce ethylene which may have a significant influence on the storage life of other fruits in the same chamber. Chemical proof now exists of the production of ethylene by apples, pears, bananas, avocados, and the fungus Pentczllium dzgzfatrrm. Biological evidence suggests that many kinds of fruit and other plant tissues do likewise. The role of ethylene in the physiology of fruits has recently been reviewed by Bide ( 1 ) and by Porritt (14).In view of the physiological role of ethylene, it was realized that a rapid method for quantitative estimation of this gas in small amounts was a prerequisite for further advance in this field. Such a method must be specific, at least for olefins, and efficient is best suited for ethylene concentrations of 0.5 p.p.m. and higher, though not more than 0.05 p.p.m. will escape absorption. Total amounts of ethylene as low as 0.2 ml. can be determined with an accuracy of 5%, while a higher accuracy can be obtained with larger amounts. Although the method is specific for olefins only, no gaseous olefin other than ethylene is known to be produced by plants. -4 number of other volatile products of plant metabolism were tested and did not interfere.enough to remove and accumulate ethylene from a moving gas stream, even though less than 0.1 p.p.ni. might be present. The available methods did not fulfill these requirements.Nelson (IS) used permanganate oxidation after presumably removing nonethylene volatiles by absorption with sodamide. In addition to questionable selectivity, the method had systemic errors, making a correction necessary. Christensen et al. ( 2 ) modified the bromination method of Davis et al. ( 3 ) for use on a micro scale, and this has been further modified by Hansen and Christensen (9) and by Hansen (8). I t has the disadvantage of maintaining the fruit samples in a static atmosphere, causing ethylene to accumulate to a concentration of a t least 25 p.p.m. Under certain conditions concentrations of this magnitude will accelerate respiratory activity and may cause increased ethylene production. Walls (19) used a wet oxidation, absorbing the ethylene from a gas stream in silver-activate...

(8,12).

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,Most studies concerning the effects of the gas composition of the atmosphere surrounding fruit have been directed toward the response of the combined changes of oxygen (3) is suggested.For the avocado, a fruit which exhibits a climacteric pattern of respiration, it was shown by Biale (2) that low oxygen reduced the respiratory activity during the preclimacteric period andl the (luration of the preclimacteric period was prolonged. Within the range of 2.5 to 21 % oxygen the time required to reach the climacteric peak was extended in proportion to the decrease in oxygen tension and the intensity of respiration at the peak was reduced. No significant stimulation of respiration wvas observed by concentrations of oxygen above 35 %. However, the cumulative carbon dioxide production from the time of picking until the climacteric peak was not changed by the treatment at any level of oxygen. In the case of the banana, another fruit with a climacteric pattern, it was found by Kidd and West ( 11 ) that storage in 2.5 and 5.0 % oxygen did not materially decrease the rate of ripening. On the other hand, Leonard (13) observed a reduction in CO, liberation by fruit stored in oxygen concentrations lower than air and no effect in concentrations higher than air.Lemons did not exhibit the climacteric pattern of respiration after picking when stored in air or at oxygen tensions below that of air, as shown in the sttudies of Biale and Young (5). The respiratory 1 Received revised manuscript Dec. 20, 1961. activity under air decreased slightly during storage. Reduction of oxygen in the atmosphere surrounding the fuit reduced the rate of respiration in proportion to the oxygen concentration in the range of 21 to 5 % oxygen. Carbon dioxide evolution increased at oxygen levels below 5 %, indicating the similarity of the behavior of lemons with other fruits characterized by a critical oxygen concentration. The storage life was extended and the (lecomposition of chlorophyll in mature green lemons was delayed by lowered oxygen.The effect of added carbon dioxide on respiratorv activity of fruits at a particular oxygen concentration has been studied little, largely due to technical difficulties. Limited data are available on the banana. By the use of the katharometer method Gane (9) observed a suppression of the climacteric and reduction of respiratory activity in an atmosphere of 10 % carbon dioxide and 10 % oxygen. Wardlaw (20) subjected unripe bananas to clifferent combinations of oxygen and carbon dioxide. On the basis of gas analysis he concluded that there was a 50 X redluction in rate of respiration over a wide range of 02 and CO2 concentrations as compared with air. His (leterminations were limited to green fruit and iwere done in a closed system in which the gaseous composition could not be kept constant. The use of analytical methods described in the first paper (21) of this series has enabled us to study the effect of carbon dioxide at several oxygen levels on the respiratory activity and storage behavior. The responses to C...

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