Hoyt: CULTURES OF SPIROGYRA 351 
less favorable, while that of Knop was distinctly unfavorable, 
probably because of its marked acidity. 
2. Both the tap water and the ordinary distilled water of the 
Heidelberg Institut were markedly toxic to this Spirogyra, even 
after distillation (or redistillation) from glass to glass. 
3. The toxicity of the tap water was partially removed by con- 
centrating the water to a fraction of its original volume, and was 
entirely removed by heating to 144° C. or by distillation in glass 
from animal charcoal; but the water was not greatly improved 
by simple distillation or by heating to 100°C. The toxicity of 
ordinary distilled water was partly or wholly corrected by the 
presence in the culture of chalk, lime, solid agar, dry sphagnum 
moss, colloidal platinum, or of other adsorbents; it was partially 
corrected by redistillation or by heating to 144° C. The presence 
in the cultures of filter paper, cotton, sand, kaolin, or CaCl, was 
without effect, and redistillation in glass from animal charcoal 
did not produce nontoxic water. 
4. The results obtained seem to indicate that the toxic ma- 
terials present in the tap water were mostly volatile (perhaps 
Organic substances derived from the soil), with a relatively small 
amount of nonvolatile material probably emanating from the 
supply pipes. The toxic substances in the ordinary distilled 
water were mostly nonvolatile (probably derived from the sup- 
Ply pipes and from the still), with a small amount of volatile 
matter carried from retort to receiver with the distillate. 
5. When nontoxic water was used, the best growth was ob- 
tained in nutrient solutions containing from 0.05 to 0.1 per cent 
of total salts; but when ordinary distilled water was used, the 
optimum concentration of similar nutrient solutions was ten times 
as great. 
6. With KNOs, KsHPO,, KCl, MgS0,, and CaCh (singly or in 
various combinations), a mixture of the three potassium salts was 
as toxic as KCI alone; KCl, MgSQu, and CaCh were all extremely 
toxic when used singly; but mixtures of any two of these three 
were less toxic than the solution of a singleone. Good growth was 
obtained only when salts of all three metals were present in favor- 
able proportions. The toxicity. of MgSO, appeared to be as 
completely counteracted by KCl as by CaCk. 
