MORPHOGENETIC EFFECTS OF DAYLENGTH IN SCHOTTERA-NICAEENSIS

The S. nicaeensis thallus exhibits, a typical secondary heterotrichy: terete perennant creeping axes and flattened annual erect fronds. The prostrate system produces new uprights in autumn, while in late spring the old blades produce marginal terete proliferations, which usually attach themselves to the substratum becoming new creeping axes. The pr esent study demonstrates that the changes in morphogenetic trends are controlled by daylength, regardless of temperature. Both the upright f ormation and the flattened growth are short day responses, whereas bot h the terete proliferation outgrowth and the rhizoid production are lo ng day responses. This seems to be the first report on two vegetative photoperiodic responses to different daylengths within a single algal species.