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Dahlia tuber. Polarised light micrograph of a section through the tuber of a Dahlia sp. plant, showing inulin crystals. The Dahlia produces root tubers that are mostly made up of scattered vascular bundles. Parenchyma tissue cells store the insoluble polysaccharide inulin as a means of storing energy. When the tubers are immersed in alcohol the inulin crystallises near bundles as spheroid crystals. Magnification: x7, when printed 10 centimetres wide. (KEYSTONE/SCIENCE PHOTO LIBRARY/DR KEITH WHEELER/SCIENCE PHOTO LIBRARY)