[Vol. 10 



228 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



In examining numerous specimens of partly rotted lemons and 

 oranges attacked by various fungi it was found that the fungus 

 had partially digested the rag, or white pithy layer inside the 

 rind, that it had attacked the walls of the carpels, the placentae, 

 and in some cases the outer layers of the rind, without releasing 

 the acid from the juice sacs themselves. Examination of some 

 oranges in an advanced state of decay showed that the walls of 

 the juice sacs had been attacked and the juice sacs broken down, 

 and the same was true in less degree of lemons rotted by certain 

 fungi. This latter condition is only the result of advanced decay, 

 however. In many cases the examination showed the rind com- 

 pletely digested, but the adjacent juice sacs still intact. Even 

 where the pulp sacs were seemingly attacked, it was only when 

 the decay had reached a very advanced stage that the fungus 

 could be demonstrated microscopically inside the juice sacs. 

 Oranges should present little difficulty, as far as acidity is con- 

 cerned, for decay fungi, and it is probably the case that the pulp 

 is readily destroyed, but it is improbable that the pulp of lemons 

 can be attacked destructively until the fungus is well established 

 in the less acid portions. 



Citric acid occurs in a large number of fruits besides those 

 included in the citrus group, and in fact citric and malic acids 

 make up the bulk of the acids of ripe fruits. Bigelow and Dunbar 

 ('17) summarized the work on the acidity of fruits and added 

 data of their own. Besides citrus fruits, most berries were found 

 to contain citric acid, and this was especially true of cranberries, 

 which are extremely acid. Tomatoes, cantaloupes, one variety of 

 pear, and a number of other fruits were also found to contain 

 citric acid. Pome and drupe fruits as a rule were found to contain 



malic acid 



metabolism 



reported upon extensively by several authors. Wehmer ('93) 

 reported on the genus Citromyces as containing acid producers. 

 He obtained good yields of citric acid in the presence of CaCO,. 

 Martin ('16), using various species of the genus Citromyces, 

 attempted to work out a commercially practicable method for 

 producing citric acid by the fermentation of sugar but obtained 

 insufficient yields. Butkewitsch ('22) studied quantitatively the 



