False colour scanning electron micrograph of spores of the field horsetail, Equisetum arvense. The horsetail is the only living type of a primitive family of plants, the Sphenopsids, that were predominant at the formation of the coal measures. The vegetative stems are produced from underground rhizomes & the leaves are reduced to toothed sheaths at the leaf joints. Fertile shoots bear conelike sporangia, carrying the spores, which in this species appear in Spring. The picture shows moist spores bound tightly by their elators, or bands of thickened cells. As the spores dry out, the elators unfurl, tossing the spores out of the sporangium. Mag: X 114 at 35mm. Original is BW print b450/025.