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. The filament is made up of elongated cells which secrete a mucilaginous substance which binds adjacent filaments. Each cell contains one or more chloroplasts, arranged in spiral bands. The chloroplasts contain green chlorophyll pigments & are sites of photosynthesis within each cell. Dark field illumination. Magnification x400 at 35mm size."