330 



MOTOR RESPONSES 



There is considerable evidence which indicates that when colonies are 

 photopositive and cathopositive, they are negatively charged; and when 

 they are photonegative and anopositive they are positively charged 

 (Mast, 1927c). If this obtains, the movement of ions in photopositive 

 colonies in a direct current would result in decrease in the negative ions 



K 







K 



K 



K 



A 



Figure 118. Diagrams illustrating the effect of direct current on the distribution of 

 ions in colonies of Volvox and their response. — , negative charge on colony; +, positive; 

 o, no charge; A, anode; K, cathode; large arrows, beam of light; small arrows, direction 

 of movement of colonies in the beam of light; curved arrows, direction the colonies turn 

 after the current is made and broken respectively. Note that there is in negatively charged 

 colonies, after the circuit is closed, a decrease in potential at the cathode, and a decrease 

 at the anode after it is opened, that the opposite obtains for positively charged colonies, 

 and that there is no change in potential in neutral colonies. (Modified after Mast, 1927b.) 



on the cathodal side. In turn, this would cause decrease in potential and 

 increase in permeability here. It would also result in increase in the 

 negative ions at the anodal side and increase in potential and a decrease 

 in permeability there (Fig. 118). The movement of ions in photonega- 

 tive colonies would result in increase in positive ions, in the potential, 

 and increase in permeability on the cathodal side. The reverse would 



