250 
WILLIAM J. ROBBINS 
amount of starch digested as compared to the water culture. In 
fact, from the loss noted in the NaH2P04 series, NaH2P04 appears to 
increase the amount of starch digested. 
Again the potassium salt permits less digestion than the sodium 
salt, with two exceptions — M/ioo,ooo concentrations at the end of 
the second week. It would appear that this failure to inhibit the 
digestion as compared to the check is due to the effect of the acid, 
not the basic, radical of these salts. 
Ca and Mg salts. — Experiments similar to the above were per- 
formed, in which the chlorides, the sulphates, and the nitrates of 
calcium and magnesium were compared. Space precludes the cita- 
tion of the actual data obtained. It will be sufficient to say that 
the results were very similar to those obtained with the potassium 
and sodium salts of the same acid radicals. The addition of M /ioo,ooo 
of either CaClo, MgCU, CaS04, or MgS04 to distilled water treated 
with carbon black is sufficient to decrease the actual amount of 
digestion. The effect of this concentration of these salts on the 
growth of the fungus is inappreciable. CaCl2, MgCU, CaS04, or 
MgS04 of a concentration M/io,ooo depresses the actual digestion 
more than does a M/ioo,ooo concentration of the same salts. The 
effect of this concentration on the dry weight of the fungus is also 
inappreciable. The amount of starch digested in M/i,ooo concen- 
tration of these salts is greater than the digestion in M/io,ooo con- 
centration, but it is not so great as in the distilled water treated with 
carbon black. M/i,ooo concentration of these four salts also in- 
creases the amount of growth. The dry weight of the fungous my- 
celium is from 0.5 to i mg. greater in the M/i,ooo concentration than 
in the distilled water treated with carbon black or in the M/ioo,ooo 
or M/io,ooo concentration of these salts. The starch digestion per 
unit of dry weight is greatest in the distilled water treated with 
carbon black, and decreases with increasing concentration of the 
salt added. The addition of Ca(N03)2 or Mg(N03)2 to a solution of 
soluble starch in distilled water shaken up with carbon black increases 
the amount of digestion. It also increases the dry weight of the 
fungus. The digestion per unit of dry weight of mycelium, however, 
is less in the presence of the salt than in the water alone, and decreases 
with increasing concentration of the salt. 
Discussion. — The results of this investigation give no support 
to the idea that potassium and calcium are intimately connected 
