384 S. O. MAST 



N alkaline. In this solution, under the conditions of the experi- 

 ment, the colonies were strongly negative. After the addition of 

 sufficient acid to make the colonies positive, the solution was 

 0.0015 N alkaline, and in a few other tests the reduction necessary 

 was even less. In some it was, however, considerably more. 

 This shows that the condition of the organism is involved in the 

 process. 



In Spondylomorum it was found that reduction in alkalinity 

 produced by the addition of distilled water had little, if any, effect 

 on the sense of orientation (Mast, '18, p. 512). Similar results 

 were obtained in Volvox and Pandorina. Both of these forms 

 live for several days in chemically pure water and respond nor- 

 mally, but only in relatively few tests was there any indication 

 whatever of reversion due to the dilution of pond water with 

 pure water, and in these tests the effect of the dilution was very 

 slight. But that there was actually an effect was shown by the 

 fact that in diluted pond water it required considerably less acid 

 to induce positive reactions than' it did in normal pond water. 

 For example, in a given test in a solution consisting of one part 

 of pond water and nine parts of pure water, it required only one- 

 third as much acid to induce reversion as it did in the pond water. 

 The dilution consequently seems to tend to make the colonies 

 positive, but not in proportion to the degree of dilution. 



If a reduction in alkalinity produces reversion from negative 

 to positive orientation, it seems reasonable to expect the reverse 

 if the alkalinity is increased by means of adding alkalis. This, 

 however, does not appear to occur. I repeatedly added sodium 

 hydrate to solutions containing positive colonies, of Volvox or 

 Pandorina, but never obtained any indication of reversion except 

 in case the alkali was added immediately after the colonies had 

 been made positive by the addition of acids, and in such cases 

 there was always some question as to the actual effect of the 

 alkali. However, an increase in the concentration of the solu- 

 tion due to slow evaporation clearly tends to make the colonies 

 negative. These results are in full harmony with those obtained 

 on Spondylomorum (Mast, '18, p. 512). 



