Tactic Movements in Chlamydomonas moewussi

Abstract

SPECIES of Chlamydomonas are generally regarded as phototactic1. For a study of certain aspects of phototaxis, Chlamydomonas moewussii (Pringsheim collection 11–16 g) was cultivated on a medium described by Hutner and Provasoli2. The algae in their culture medium were placed in cuvettes which were illuminated from the side. Under these conditions, phototactic algae move rapidly to the illuminated side of the cuvette. The species studied showed no such phototaxis, but invariably moved to the water–gas interface. If the cuvettes were covered with olive oil, the algae moved through the oil layer to the interface. The gas phase was therefore altered. Square glass cuvettes (v. 35 ml.) were filled with 15 ml. algal suspension and fitted with rubber stoppers with in and outlet tubes. The gas phase (20 ml.) of each cuvette was flushed with 2 litres of gas mixture and the cuvettes then closed. The cuvettes were then placed under conditions of unilateral illumination. In parallel experiments, algae of the same age and culture were used. Table 1 summarizes the results of the different treatments.