462 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9, 
The growing of strictly parasitic fungi in synthetic culture solutions 
has not come into general practice. On the contrary, various circum- 
stances have led to the general use of plant decoctions. Such media are 
excellent for certain purposes, but for physiological work media of known 
composition are almost indispensable. 
In an attempt to formulate a synthetic solution for the growth of 
parasitic fungi, the roles of the so-called essential inorganic elements along 
with that of calcium and zinc were studied. For this work Richards' 
solution was used as a standard and for the deviations. The inorganic 
constituents were replaced by non-essentials, the concentrations and 
balance being maintained as nearly as possible. In addition, eight sugars 
were used. The possible importance of the presence of minute quantities 
of zinc and of other substances was recognized, and special precautions were 
taken in selecting glass of tested solubility and in its thorough cleaning. 
Erlenmeyer flasks of 150-cc. capacity were employed. The water used 
was stock distilled water redistilled through a Branstead still. The chem- 
icals were obtained from the J. T. Baker Chemical Company and from the 
lot prepared for the use of the National Research Council in nutrition 
studies of higher plants. The arrangement of the experiment is given in 
table I. In each flask was placed 50 cc. of the nutrient solution, and each 
solution was set up in three sets of triplicates. The solutions were sterilized 
by heating in an autoclave 30 minutes at 10 pounds' pressure. One series 
of flasks was inoculated with Fusarmm oxysporum, another with Rhizopus 
nigricans, and a third with Aspergillus niger. After the flasks were inocu- 
lated, they were placed at room temperature and the organisms were 
allowed to grow for 16 days. At the end of this period the mycelium and 
spores were collected on previously dried and weighed filter paper, dried 
to constant weight in a steam oven at 97° C, and reweighed. Results are 
recorded in table i. 
The results of this experiment indicate that calcium exerts a stimulative 
action on the growth of the three organisms used. The exact manner in 
which calcium influences growth is problematical. However, it can be 
logically concluded that its role of counteracting acidity in higher plants 
plays an important part in the growth of these fungi, especially in that of 
Aspergillus niger and Rhizopus nigricans, two acid producers. To make 
certain that the increased weight was due to fungous growth and not to 
calcium oxalate crystals, the mycelium was treated with alcohol and thirty 
percent hydrochloric acid and redried. The treatment resulted in no 
appreciable decrease in weight of the fungous material grown with calcium 
present, as compared with the cultures grown without calcium. The 
quantity of acid produced by the growth of Aspergillus niger and Rhizopus 
nigricans is proportional to the amount of fungous material produced. 
With available carbon, growth continues until stopped by the hydrogen-ion 
concentration. If the acid is neutralized, Rhizopus nigricans will grow until 
