POWER AND SYRED / SCIENCE PHOTO LIBRARY POWER AND SYRED / SCIENCE PHOTO LIBRARY
Light micrograph of the spores (brown spheres) of the field horsetail, Equisetum arvense, surrounded by a tangle of filamentous structures known as elators. The spores develop with the elators wound tightly round them, but when the spores are mature, the elators dry out and unwind rapidly, tossing the spores out of the spore sac. Although all the spores look alike, they germinate to produce two types of prothalli; large female ones or smaller male ones. The horsetails are the only living representitives of a primitive family of plants, the Sphenopsids, that were predominant at the time of the formation of the coal measures. Magnification: x200 at 35mm size.
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