May x6, 1921 Respiration of Sweet Potato Storage-Rot Fungi 223 
to shown by many investigators that fungi frequently increase the acidity 
of the substratum. Wehmer’s (20, 21) work in this direction is signi¬ 
ficant. He found that Aspergillus niger rendered the solution at first 
acid. The acidity (oxalic acid) gradually increased to a maximum and 
declined once more during the next few weeks to zero, the solution 
finally becoming alkaline. The fungus was found to decompose free 
oxalic acid at the higher temperatures. He likewise showed that the 
amount of acid formed was not necessarily associated with the quantity 
of fungous growth produced. The acid is found only when the sub¬ 
stratum gives no acid reaction and when the organism is cultivated in 
sugar, proteid, glycerin, oil, and salts of organic acids. Wehmer also 
found that Citromyces glaber Wehm. can utilize the citric acid which it 
has produced. Furthermore, although this organism will tolerate a 
concentration of 20 per cent citric acid, it only produces enough to render 
the substratum 4 per cent acid. In a discussion of his results he calls 
attention to the fact that the only acids formed by Aspergillus or Peni- 
cillium in notable quantities are oxalic and citric. Botrytis cinerea and 
Rhizopus nigricans and some other fungi produce oxalic acid only in 
traces and only in a nearly neutral medium. An abundant carbohy¬ 
drate supply and calcium salts, such as calcium phosphate or carbonate, 
favor its production. Kunstmann (14) found that oxalic acid was pro¬ 
duced in all the media used by him but that at the end of the experiment 
it never exceeded 0.05 gm. in 100 cc. of solution. Molliard (15) > however, 
found that Sterigmatocystis nigra v. Tieg. produced both citric and 
oxalic acid, together or alone in the medium in which saccharose was used 
as the source of carbon. Citric acid was more abundantly produced 
than oxalic, but both increased gradually up to the end of the experi¬ 
ment. The acid production of a large number of species of Penicillium 
was studied by Currie and Thom (4), who found that it was formed in 
varying amounts by all of them and in a large quantity by one species 
in particular, Penicillium oxalicum Currie and Thom. According to 
these investigators the oxalic acid produced is not an end product. It 
reaches its maximum in 8 to 12 days and then declines. The results 
of the writers’ experiments show that in no case was enough C0 2 pro¬ 
duced to account for all the sugar consumed. Undoubtedly some of 
the sugar was converted into other compounds, and in this connection 
alcohol, aldehydes, and organic acids suggest themselves as the most 
likely. The presence of alcohol was demonstrated in the culture solu¬ 
tion in which the fungus grew in the case of four organisms and not 
in the controls. In another paper it was shown that these same organ¬ 
isms growing in the solution used in these experiments increased the 
hydrogen-ion concentration. It seems, therefore, that alcohol or acids 
or both may have been produced in the solutions. 
