Seventeen non-motile strains of Chlamydomonas reinhardii isolated by Dr Lewin and thirty-six newly isolated strains have been examined in the electron microscope for structural abnormalities of the flagella. Fourteen of them have straight, paralysed flagella in which the central fibres are replaced by an irregular core of disorganized material. The fourteen mutations map at four unlinked loci. Some of them are leaky; light and electron microscope observations on leakiness are described. In the former case leakiness is measured by the proportion of motile cells, and in the latter by the proportion of intact centre fibres seen in transverse sections. The degree of leakiness is to some extent characteristic of particular loci.
A partial suppressor of some of these mutations has been isolated which acts on all the mutant alleles at two loci and to a much lesser extent on four out of five alleles at a third locus.