AMERICAN JOURNAL OF BOTANY 
[Vol. 8 
are doubtless in part due to the deposit of calcium oxalate crystals on the 
hyphae in the Ca(N03)2 series, but the differences are apparently too great 
to be entirely attributed to this cause. The reduced yield in the NaNOs 
group may in part be the result of a toxic influence of the Na, as seems to be 
indicated by the reduction in yield in the cultures containing the largest 
amounts of NaNOs. This reduction in yield is indicated by the downward 
trend of the upper end of the curve representing series 5 (fig. 5). There is 
also a possibility that the absence of Ca has somewhat depressed the yields 
in the NaNOs group. Although it has been demonstrated that calcium is 
not essential to the growth of fungi, it may still be beneficial as an antago- 
nizing influence in some such manner as has been suggested by Osterhout (5), 
who states that 
The classical researches of Pasteur and RauHn and the later work of other investi- 
gators have shown that calcium is not needed for the nutrition of fungi, and it is, therefore, 
omitted from culture solutions for these plants. This answers very well as long as the 
solutions are sufihciently dilute. I find, however, that when the concentration of the solu- 
tion is increased it becomes toxic, and the addition of calcium then produces a remarkable 
improvement in growth. Calcium, therefore, has a protective value for fungi just as for 
other plants, though not needed for nutrition. 
Summary 
Aspergillus niger was grown on three-salt solutions of total concentra- 
tions equivalent to 0.5, 2.1, and 4.2 atmospheres respectively. For each 
total concentration 36 solutions were made, representing all the possible 
combinations obtained by varying the partial concentrations of each of 
the salts by increments of i/io of the total concentration. 
A number of solutions in which the salt proportions and total salt 
concentration remained the same, but with sugar concentrations varying 
from I to 8 atmospheres by increments of one atmosphere, were also tested. 
1. In solutions all with the same salt proportions, an increase in total 
concentration gave a corresponding increase in yield. 
2. The partial concentrations of KH2PO4 and MgS04 were varied within 
wide limits without in any way affecting the yields. 
3. Yield in dry weight of fungus is approximately proportional to the 
amount of NO3 present in the culture, whether this is produced by increasing 
total concentration and leaving salt proportions unchanged, or by changing 
salt proportions and leaving total concentration the same. 
4. With a sugar solution having an osmotic concentration value of 
three atmospheres, the limit of growth in the Ca(N03)2 cultures was between 
0.9 gram and i.o gram, regardless of the amount of salts present. 
5. In cultures with constant salt proportions and total salt concentra- 
tions but with varying sugar concentrations, the dry weights of fungus were 
very nearly proportional to the sugar concentrations of the cultures. 
Laboratory of Plant Physiology, 
New Jersey Agricultural Experiment Station 
