PHYSIOLOGICALLY ACTIVE GAJSES 165 



in the absorbent. He found ^^ that green Bon Chretien pears stored at 

 0° C (32° F) produced vapors that ripened bananas. Denny and Miller ^^ 

 and Denny ^^^ ^^' ^* found that most of the many kinds of living plant 

 tissues tested emanated a chemical that induced leaf epinasty in the 

 potato. Among the tissues giving the response were fruits (mature and 

 green), seeds, flowers, leaves, leafy stems, young shoots, roots, tubers, 

 anthers, pistils, and petals of a number of different kinds of plants. A few 

 living tissues gave negative results: potato tubers (whole or cut into 

 pieces) ; seedlings of wheat, corn, and oats; mycelium of Rhizopus nigricans, 

 two mushrooms, and baker's yeast. By absorbing emanations from a 

 greater number of seedlings of oats, wheat, corn, and several other seedlings 

 in a mercuric nitrate-nitric acid reagent and later releasing the absorbed 

 gases with HCl, a positive response was obtained. It may be that all living 

 plant tissues produce ethylene, but some in very low amounts. Ripe apples 

 produce relatively large amounts. The flesh of the squash and dandelion 

 flowers are less active. Seedlings of Cruciferae tested produced both toxic 

 (probably mustard oils) and leaf epinasty-induciag emanations. Denny 

 found that tomato stems lq the horizontal position, out of equilibrium with 

 gravity, produced more of the effective emanations than smiilar stems in 

 the vertical position. 



Quantitative determinations have been made of the amount of ethylene 

 produced by fruits and contained in fruits, as well as of the effect of stage of 

 ripening and other conditions upon the amount of ethylene produced. 

 Niederl, Brenner, and Kelley ^^ converted the ethylene from ripening 

 bananas to acetylene and determmed the latter as silver acetylide. They 

 estimate that 100 pounds of bananas produce 0.1 to 0.2 cc of ethylene dur- 

 ing the ripening period. Nelson ^^ finds that Mcintosh apples after nine 

 months of storage contain 0.12 mg of ethylene per kilogram of apples. He 

 also found ^^ that for six varieties of apples studied, the ones with longer 

 storage lives showed less capacity to produce ethylene. There is a general 

 correspondence between the ethylene content and respiratory activity of 

 apples. Ethylene has a hydrolytic action on ripening fruits, but the effect 

 is probably not directly upon the enzymes. Ethylene may be consumed as 

 well as produced by the ripening bananas. 



Hansen ^^' P-55&-557 summarizes his quantitative measurements of ethylene 

 production by pears in part as follows: "In fruit in air at 20° C the rate of 

 ethylene production increases during the climacteric rise in respiration, 

 reaches a peak at the respiratory climax, then declines during the post- 

 climacteric period. During the climacteric rise, ethylene production in- 

 creases seven- to eighty-fold, while rate of respiration approximately 

 doubles. Each variety was found to have a characteristic maximum rate of 

 production. The maximum rate for Bartlett, a variety which maintains its 

 capacity to ripen for only a short period of time when kept at a storage 

 temperature of 0° C, is 3.25-i.48 ml per kg-day. The maximum rate for 

 Anjou, a variety which maintains its capacity to ripen for a long period of 



