Light micrograph of filaments of Spirogyra, a green alga which forms slimy threads called water- silk" or "mermaid's tresses" in stagnant or slow moving water, becoming abundant in spring or autumn. The filaments are made up of elongated cells which secrete a mucilaginous substance which binds adjacent cells. Each cell contains one or more chloroplasts, arranged in spiral bands. The chloroplasts house the green chlorophyll pigments and are sites of photosynthesis within each cell. Magnification unknown."