1. The view recently expressed that “physiologically balanced solutions have not een made use of by botanists, ” can hardly be sustained, since Knop's ulture solution must be regarded as such a solution. Lower forms of algæ and fungi do not require physiologically balanced solutions. 2. Potassium sulphate and nitrate are only injurious for plants when the concentration is abnormally high. Potassium chlorid at 0.3% exerts after several weeks a slow injurious effect on Spirogyra, but on Phenogams not for many weeks, even at 0.5%. The final death of Spirogyra cells in dilute solutions of potassium sulphate or nitrate is merely due to the one sided nutrition and exhaustion.- 3. Potassium salts can retard but not prevent the toxic effects of magnesium salts. The cause of this retardation is entirely different from the prevention of this toxic action by calcium salts. 4. Some interesting observations may be made on Spirogyrakept in imperfect culture solutions. Thus, e.g., in a solution containing only KCl and MgCl2 the cytoplasm can remain long alive after the nucleus is killed, recalling GERASSIMOW'S cells without a nucleus; in a solution containing only K2SO4 and CaSO4 abundance of rhizoids is formed. This rhizoid formation depended in our cases only upon the salts in solution, while in other cases it depends upon the contact with an object, as BORGE and KNY have observed. In saturated gypsum solution the tendency to show geotropism is strongly preserved and the cells continue to produce an abundance of starch even after the chloroplasts have gradually turned yellow. This starch formation can be considered as proof that neither potassium nor magnesium of the chloroplast had been replaced by calcium. This yellowing is not observed in the solution of 0.2% CaCl2 even after three months. 5. Interesting effects can be observed with Spirogyra kept in full, but not balanced culture solutions.