A MORPHOLOGIC AND GENETIC STUDY OF GONIUM PECTORALE

Abstract

THE MOST FREQUENTLY encountered species of Gonium is the 16-celled G. pectorale Muller, which was one of the original species described by 0. F. Muller in 1773 when he erected the genus. By 1838 it was the only species still considered to be a member of the genus, and it thus became the lectotype of Gonium (Ehrenberg, 1838). Previously, Bory (1824) had described a new monotypic genus, Pectoralina, whose type, P. hebracia, Ehrenberg (1838) and others have considered synonymous with G. pectorale. In 1866 Diesing placed G. helveticum Perty in his new genus Glenogonium, but Warming (1876-77) and Biitschli (1884) have referred this species to G. pectorale. Pocock (1955), in her study of the genus Gonium in North America, considered G. pectorale as comprised of two varieties, variety pectorale and variety praecox. The variety praecox has comparatively small, usually pale-green colonies composed of slightly elongated cells with the apex wider than the base. This varietal name refers to the precocious development of daughter colonies, while the mother colony is still quite small. GENERAL TECHNIQUES. Throughout this investigation, single colony isolations were made with a glass capillary pipette using a dissection microscope equipped with substage, darkfield illumination. The cultures were maintained in Pringsheim's soil-water medium (Starr, 1956) or in a modified Beijerinck's medium (table 1) to which were added 10 per cent soil-water supernatant and 1-1.5 per cent agar. Active growth of the cultures occurred at 200C. at 200250 ft.-c. intensity (provided by 40-w. cool-white fluorescent lamps) on a 16 hr. light-8 hr. dark cycle. Stock cultures received illumination of about 75 ft.-c. intensity and were transferred every 6-8 weeks. The strains used in this study were obtained from field collections and from soil-cultures. The latter were made by covering dry mud samples in a dish with glass-distilled water and placing the dishes under the conditions described above. The colonies were isolated 1-4 days after the water had been added. Colonies isolated from one collection site at any one time are considered members of the same