/nos"tok/, n.any freshwater, blue-green alga of the genus Nostoc, often occurring in jellylike colonies in moist places.[1640-50; < NL, coined by Paracelsus]
* * *The cells are arranged in beadlike chains grouped together in a gelatinous mass. Ranging from microscopic to walnut-sized, nostoc masses may be found on soil and floating in still water. A special thick-walled cell has the ability to withstand drying for long periods of time. After 70 years of dry storage, cells of one species can germinate into filaments when moistened. Like most other cyanobacteria, nostocs contain two pigments and are capable of nitrogen fixation.
* * *▪ algaegenus of blue-green algae with cells arranged in beadlike chains that are grouped together in a gelatinous mass. Ranging from microscopic to walnut-sized, masses of Nostoc may be found on soil and floating in quiet water. Reproduction is by fragmentation. A special thick-walled cell (akinete) has the ability to withstand desiccation for long periods of time. After 70 years of dry storage, the akinete of one species germinates into a filament when moistened. Like most blue-green algae, Nostoc contains two pigments, blue phycocyanin and red phycoerythrin, as well as chlorophyll, and has the ability to fix nitrogen in specialized cells called heterocysts. A terrestrial species has been used as a supplementary food source in Asia.
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