Mutants affecting vegetative cell orientation in Volvox carteri

The vegetative cells of Volvox are highly oriented with respect to each other and to the spheroid on which they occur. Mutants have been isolated which affect this orientation either directly or indirectly. Mutants affecting flagella (flg), including a temperature-sensitive mutant, demonstrate that flagella must be present during or following embryo inversion for proper cell orientation. Other mutants (eye) which have apparently functional flagella lead to the conclusion that the presence of functional flagella is not sufficient for proper cell orientation. These mutants also demonstrate the necessity of proper cell orientation for the phototactic motion of the spheroid.