190 
Journal of Agricultural Research 
Vol. XXI, No. 4 
its susceptibility to disease. At the time these investigations were 
initiated by the writers there were little available data regarding the 
sugar requirements of the particular fungi responsible for the decay of 
sweet potatoes in storage. Since glucose is probably the most readily 
available carbohydrate in the sweet potato for a majority of the fungi 
to be studied, experiments were designed to determine to what extent 
this sugar is utilized as a source of carbon by the following organisms: 
Fusarium acuminatum E. and E. emend. Wollenw., Diplodia tubericola 
(E. and E.) Taub., Rhizopus tritici Saito, Mucor racemosus Fes., Sclero- 
tium bataticola Taub., Penicillium sp., Botrytis cinerea Pers., and Spha- 
ronema fimbriatum (E. and H.) Sacc. 
EXPERIMENTAL METHODS 
culture media 
Many different synthetic culture media have been used by investi¬ 
gators while studying the physiology of fungi. When the present inves¬ 
tigations were begun, Czapek’s nutrient solution, together with several 
others, were tested, but none proved entirely satisfactory. In trial 
experiments with Rhizopus tritici it was found that when ammonium 
nitrate was substituted for sodium nitrate and glucose for cane sugar in 
Czapek’s solution a vigorous growth resulted. Other storage-rot fungi 
responded similarly. Hence, 1.6 gm. of ammonium nitrate were used 
instead of the 2 gm. of sodium nitrate required per 1,000 cc. in Czapek’s 
solution. The solution as finally employed was prepared as follows: 
Magnesium sulphate (MgS 0 4 ).., 
Potassium phosphate (K 2 HP 0 4 ) 
Potassium chlorid (KC 1 ). 
Ferric sulphate (FeS0 4 ). 
Ammonium nitrate (NH 4 N 0 3 ).. 
Distilled water. 
0.5 gm. 
1.0 gm. 
•5gm« 
.01 gm, 
1.6 gm. 
1,000 cc, 
Only C. P chemicals were used in preparing this solution. 
That fungi differ in their requirements as to the source of nitrogen, as 
well as carbon, has been suggested by the results of many investigators. 
Laurent. (20) found that Alternaria tenuis Nees, Mucor racemosus Fres, 
and Aspergillus glaucus Link, grew well on solutions containing nitrates. 
Aspergillus niger v. Tieg., on the other hand, although it can utilize nitrates 
as a source of nitrogen, thrives better on ammonia. It is claimed by some 
investigators that a combination of peptone and glucose gives the best 
results with most fungi. Went (31) found that this combination was 
preferable to all others for Monilia. Czapek (5), on the other hand, 
showed that the amino-acids in association with glucose are preferable 
to peptone for Aspergillus, and Fischer (<?) found that Bacillus coli 
Fsch, B. subtilis (Ehren) Cohn, and B. pyocyanus Gess, could use nitrate 
in association with glucose, but if glycerin was substituted for the glucose 
the latter organism alone thrived. Dox ( 6 ) found that species of Asper- 
