Green spores of Equisetum diffusum D. Don (Equisetaceae). The spores of this group of ferns have four strap-like appendages, called elaters, that coil and uncoil in response to changes in humidity. When the air is dry the elaters extend outward and create wind resistance for spore dispersal. When its humid, they coil around the spore so that buoyancy decreases and the spore drops onto moist soil.