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AMERICAN JOURNAL OF BOTANY 
[Vol. 8 
itself. The stimulative effect of high partial concentrations of KH2PO4 
he attributes to the increased acidity in these cultures. In media containing 
traces of iron and zinc an increase in acidity failed to give further stimulation. 
From these results of Steinberg it seems probable that the iron added to 
the media used in the experiments herein reported was sufficient to give 
"maximum stimulation," and that as a consequence the MgS04 and KH2PO4 
salts could not produce the stimulative effect which they produced in 
Steinberg's iron-free medium. 
In direct contrast to the indifferent effect of changes in the partial 
concentration of KH2PO4 and MgS04 is the effect of changes in the partial 
concentration of the nitrate salts. On the triangular diagrams of series 
I to 5 (figures 3 and 4) it will be observed that for each of the series there is a 
uniform increase in yield values in passing from the left to the right margin 
of the triangle representing the series; that is, as the proportion of the 
nitrate salt increases, there is a corresponding increase in the yield values. 
In series i, for example, in those cultures in which Ca(N03)2 furnished only 
i/io of the total salt concentration (Ci cultures) the yields are very low, 
varying between 0.055 0.065 gram. Where the Ca(N03)2 is increased 
to 2/10 of the total concentration (C2 cultures) the yields are almost doubled, 
the values being between o.ioi and 0.119 gram for these cultures. Like- 
wise, throughout the entire series an increase in Ca(N03)2 is followed by a 
corresponding increase in yield. Thus, culture R1C8, which has the highest 
nitrate content of any culture in the series, has also the largest yield (0.328 
gram). This same close correlation between the partial concentration of 
NO3 and yield is shown for all the series, the only apparent exception being 
in the high-yielding cultures of series 3 and 5 in which the exhaustion of the 
sugar supply limited further growth. 
The relation between the partial concentrations of NO3 and yields is 
brought out very clearly in figure 5, which shows the dry weight yields 
plotted against NO3 content of the cultures. In these graphs the abscissas 
represent grams of NO3 per liter of culture medium, and the ordinates repre- 
sent grams dry weight of fungus per culture. Each dry weight represents 
the average of all cultures of a single series containing equal quantities 
of NO3. 
It will be observed that the curves representing series i, 2, and 3 (Ca 
group) are very nearly coincident, indicating that all cultures within this 
group which contain equal quantities of NO3 have approximately the same 
yield values regardless of the total salt concentration or of the amounts of 
KH2PO4 and MgS04 present. This fact is brought out very clearly if a 
direct comparison is made between the yield values from cultures with the 
same NO3 content but having different total concentrations. Thus, 
culture R1C8 of series i , all the C2 cultures of series 2, and all the Ci cultures 
of series 3 contain approximately the same amount of NO3 per liter, but 
differ widely in their total salt concentrations. Culture R1C8 of series I 
