LIFE HISTORY STUDIES OF THE PACIFIC COAST MARINE ALGA, COLLINSIELLA TUBERCULATA SETCHELL AND GARDNER

Abstract

Culture studies of a marine green alga, described from the Pacific Coast of North America as Collinsiella tuberculata Setchell and Gardner, have shown it to be a stage in the life history of a form of Enteromorpha intestinalis (L.) Link. The Collinsiella-stage is thought to be the sexual phase, or a basal remnant of the Enteromorpha-stage, and produces biflagellate gametes. The typical tubular thallus of Enteromorpha has been grown in culture from zygotes of the Collinsiella-stage and zoospores of the Enteromorpha-stage. Parthenogenetic development of gametes is also indicated. Some of the tubular plants produce biflagellate gametes which cannot be distinguished from those of the Collinsiella-stage. Others produce quadriflagellate zoospores, which may be meiospores or mitospores. An accessory method of reproduction by quadriflagellate mitospores (neutral spores) occurs and this asexual cycle has been carried through three successive generations in culture without an intervening sexual phase. Tubular thalli of Enteromorpha inteslinalis (L.) Link producing biflagellate gametes during the spring and early summer and quadriflagellate zoospores during the late summer are found in nature in the same area from which the Collinsiella-stage was obtained. These are believed to represent in nature the normal sexual life cycle of this plant, which has been reported to have an alternation of isomorphic generations. The possible relationships between the stages obtained in culture and those observed in nature are discussed. A number of hypothetical conclusions have been drawn with respect to the systematic position of the genus Enteromorpha and related genera. These studies are being continued to clarify several unknown aspects brought out by this preliminary study. A cytological study is being undertaken to substantiate the conclusions drawn from the morphological data.