210 BOTANICAL GAZETTE [MARCH 
carried out with plants from the same original -stock but kept for 
some time under different cultural conditions. In experiments 
designed to test the effect of special environmental conditions upon 
organisms it is absolutely necessary to guard, as far as may be pos- 
sible, against these different physiological states in the material 
employed. Such a statement is self-evident, yet many results and 
criticisms found in physiological literature seem to have been 
brought into existence through failure to take this fundamental 
condition sufficiently into account. 
The author is greatly indebted to Professor Gzorc KLEss for 
the privileges of his laboratory and for many helpful suggestions, to 
Professor GEorG Brepic and Dr. W. FRAENKEL for their kindness 
in furnishing the colloidal solutions employed in this study, and to 
Professor B. E. Livincston for helpful advice in the preparation of 
this paper. 
Summary 
t. Colloidal silver was fatal to filaments of Spirogyra in all con- 
centrations above 0.045 ppm. and was injurious in concentrations 
as low as 0.00225 ppm. The weaker solutions of silver were ren- 
dered almost or entirely non-toxic, during the period of the experi- 
ments, by addition of colloidal platinum, animal charcoal, or 
inorganic salts to form a 0.5 per cent Crone’s solution. 
2. A solution containing 90 ppm. of colloidal gold and approx!- 
mately 0.02 per cent of NaOH was only very slightly injurious. 
3. A solution containing 96 ppm. of colloidal platinum was 
almost non-injurious during the period of the experiments, and, in 
less concentrated solutions, partially corrected the toxicity of tap 
water, ordinary distilled water, and solutions of KCl, MgSO,, and 
colloidal silver. 
4. Colloidal gold, colloidal platinum, and, to a less extent, 
colloidal silver, in low concentration, all partially prevented injury 
to the alga filaments by toxic solutions of NaOH. Addition of 
AuCl, to a toxic solution of NaOH, or of PtCl, to a toxic solution of 
MgsO, did not render the hydrate solutions less toxic. 
5. When Spirogyra was placed in a solution containing colloidal 
platinum or colloidal gold together with NaOH, the outer portions 
of the cell walls swelled, forming crumpled, gelatinous sheaths 
