Aug. i, 1921 Changes Caused in Sweet Potatoes by Rhizopus tritici 631 
suggested the possibility that some of the reducing sugars may have 
been utilized in the manufacture of sucrose. From the results of these 
investigations, however, it will be necessary to search elsewhere for an 
explanation, since the cane sugar as well as the starch content was 
reduced. 
In investigations of this type where microorganisms are involved, 
several possibilities may be advanced to account for the loss of the car¬ 
bohydrates in excess of that required to satisfy the C 0 2 given off. First, 
a portion of it undoubtedly was utilized in the construction of fungous 
material. No measure could be made of the fungous material formed, 
and although a considerable amount of mycelium was produced the 
actual dry weight would be small. Second, Harter and Weimer (6) 
showed that in Czapek’s nutrient solution with glucose as the only avail¬ 
able carbohydrate Rhizopus tritici and other fungi produced a measurable 
quantity of alcohol. Similar results have been obtained by other 
investigators with other fungi. In some cases as much as 8 per cent 
alcohol was produced. Probably the physiological reaction of a fungus 
is different when grown on a sweet potato and on an artificial medium. 
However, if alcohol was produced in the one case there are reasons to 
suspect that it might be formed also in the other. As a matter of fact, 
the writers have demonstrated by the use of the iodoform test the presence 
of alcohol in rotted sweet potatoes. Third, acid production has been 
demonstrated by many investigators, especially when nutrient solutions 
were employed. Cooley (3) found that Sclerotinia cinerea (Bon.) 
Schroet. formed oxalic acid when grown upon peach juice, and Hawkins 
( 8 ) that the acid content of the rotted half of the peach, when decayed 
by the brownrot fungus, was higher than that in the sound half. Behrens 
(j), on the other hand, found that the acid content of the sound portion 
of an apple was higher than that of the rotted half. Hydrogen-ion 
determinations were made of the expressed juice of some of the rotted 
and decayed halves used in these experiments at the close of the respira¬ 
tion period. The results of the determinations of the samples in two 
experiments gave a P u of 3.71 and 3.695 for the rotted and 5.44 and 
5.032 for the sound. 
That acids are produced in considerable abundance seems quite 
evident, and that alcohol is formed seems probable. The carbohydrates 
required for the manufacture of acids and alcohol, together with that util¬ 
ized directly in the production of fungous material, will probably account 
to a large extent for the decrease in the sugars and starch which are not 
accounted for by the C 0 2 evolved. 
The foregoing results show that the cane sugar disappears at least in 
part from the sweet potato when decayed by Rhizopus tritici , indicating 
that it was either used directly by the fungus or converted by the host 
into some other compound, possibly reducing sugar. Studies of the 
