CITRIC ACID AS A SOURCE OF CARBON FOR CERTAIN 



CITRUS FRUIT-DESTROYING FUNGI 1 



ARTHUR FORREST CAMP 



Formerly Rufus J. Lackland Research Fellow in the Henry Shaw School of Botany 



of Washington University. 



Introduction 



The work reported here was undertaken with the idea that 

 the fungi which rot citrus fruits probably show some peculiar 

 metabolic adaptations to life in such an acid environment as that 

 furnished by the citrus fruits in general and particularly by 

 lemons. In the progress of the work, however, the available 

 methods, especially those for the quantitative determination of 

 citric acid, were found to be so unsatisfactory that it was deemed 

 advisable to spend considerable time in studying possible methods 

 and their application to the routine work of physiological experi- 

 mentation. In the first part of this paper, therefore, considerable 

 space is devoted to the methods utilized in this research as well 

 as to some notes on the chemistry and occurrence of citric acid. 

 In the execution of the physiological side of the work the utiliza- 

 tion of citric acid as a source of carbon for fungi is the special 

 phase considered, and only passing attention : 

 other important phase, the production of acid 



It is not the intention to nrooose the 



that 



intention to propose the idea that citric acid 

 tolerance or utilization is the primary factor in the invasion of 

 citrus fruits by fungi; in fact, due to the structure of these fruits, 

 it is probable that a number of parasitic fungi which cannot grow 

 in a synthetic medium as acid as the expressed juice of lemons or 

 grapefruit are still able to rot these fruits with comparative ease. 

 From a microscopic examination of numerous rotted fruits and 

 from the laboratory experimentation, the idea has been gleaned 

 that in the primary infection and rotting of citrus fruits the ability 

 to hydrolyze cellulose, and not tolerance of citric acid, is likely 



1 An investigation carried out at the Missouri Botanical Garden in the Graduate 

 Laboratory of the Henry Shaw School of Botany of Washington University and 

 submitted as a thesis in partial fulfillment of the requirements for the degree of 

 doctor of philosophy in the Henry Shaw School of Botany of Washington University. 



Ann. Mo. Bot. Gakd., Vol. 10, 1923 



(213) 



