Photo‐inhibition of cell division and growth in euglenoid flagellates

Visible light of moderate intensity causes two and perhaps three types of division inhibition in Euglena gracilis are related cells. Fluorescent light causes a general inhibition of growth and division which is temperature‐dependent. Pigmentation or complex organic media partially lifts this inhibition. A second type of inhibition, which is transient, can be caused by either fluorescent or incandescent light, and is found with an irreversibly bleached strain of Euglena grown on a limiting concentration of acetate; this inhibition could not be demonstrated in cells grown on limiting concentrations of glucose.