224 Journal of Agricultural Research voi. xxn. no. 4 



Although the old observations and experiments of Dessaignes (7) and 

 of Liebig ( //) showed that succinic acid was formed from malic acid when 

 calcium malate was present in mixtures being fermented by yeast, never- 

 theless succinic acid is generally found in plants in such small quantities 

 and always so intimately associated with asparagin that it is now cus- 

 tomary to look upon it as a degradation product of protein rather than 

 as directly related in metabolism to the other plant acids. The possi- 

 bility of amino compounds giving rise by enzym action in the plant to 

 succinic acid is sufl&ciently indicated by such discoveries as that of 

 Ehrlich (8), who has traced the production of succinic acid by yeast to 

 the fermentation of glutamic acid, and of Harden (jo), who has shown 

 that putrefactive bacteria {Bacillus coli communis), in the presence of 

 glucose, will transform aspartic acid almost quantitatively into succinic 

 acid. However, it must be stated that the whole subject of the place of 

 succinic acid in metabolism is much in need of investigation. It would 

 be a decided step forward to show that it is possible for malic acid to be 

 transformed directly into succinic acid by enzym action, as appears to 

 have taken place by autolysis in the crab apple. 



We wish to indicate the possibility that such a transformation takes 

 place and to point out that green fruits containing malic acid afford ideal 

 material for a study of the problem. We do not wish, however, to give 

 the impression that the possibility of fermentation by microorganisms 

 was absolutely excluded in our work. 



To anyone who may be inclined to take up the problem of acid trans- 

 formations in green fruits, a word of caution may not be amiss with regard 

 to the statements that have crept into general reference books such as 

 those of Czapek {6, p. 434) and Wehmer (14) with regard to the distri- 

 bution of succinic acid in plants. It is recorded from a number of unripe 

 fruits but has actually been isolated or satisfactorily identified in very 

 few cases. In 1876 Brunner and Brandenburg (2) isolated it from the 

 juice of uiu-ipe grapes (Viiis vinifera L.) . The source of most subsequent 

 reports is a paper published in 1886 by Brunner and Chuard (5). These 

 authors called attention to the earlier observation of Buignet (4) that 

 the juice of green fruits is capable of absorbing a large amount of iodin, 

 which enters into chemical combination with some constituent of the juice. 

 At the same time, a precipitate is formed, which Buignet erroneously 

 supposed to be the iodin compound. Brunner and Chuard, taking up 

 the problem at this point, showed that the iodin compound remained in 

 solution; and they obtained evidence which satisfied them that it was a 

 glucosid of monoiodosuccinic acid, derived from a naturally occurring 

 glucosid of succinic acid. Their investigation covered a considerable 

 number of green fruits and plant juices; and they actually isolated suc- 

 cinic acid, as such, from unripe gooseberries and from the petioles of 

 rhubarb. In the other instances it was merely inferred from analogy 

 that the supposed succinic acid glucosid was present. The procedure 



