Cycads

Cycads, an order of Gymnospermous plants in several respects closely related to ferns, which, though now only including some seven genera and about fifty species, played a leading part in the vegetation of Lower Secondary times. They have tap-roots; columnar, generally unbranched, stems, of no great height, with a large pith and broad medullary rays, and marked externally by leaf-scars; terminal crowns of large rigid pinnate circinate leaves, which, it has been suggested, however, may have some of the characters of branches; and dioecious flowers with elongated axes, closely resembling the sporangiferous "spikes" of some of the higher cryptogams. The male flowers consist of peltate sporophylls (stamens) in whorls, like those of Equisetum, bearing numerous microsporangia (pollen-sacs), the microspores (pollen-grains) in which are distinctly multicellular, having a group of "included cells," or male prothallium. The female sporophylls vary, those of Cycas being pinnate leaves with their lower lobes transformed into large ovules (macrosporangia), whilst those in other genera are peltate and bear only two ovules each. The seeds are albuminous, and the number of cotyledons varies. Most cycads form large quantities of starch in their pith, from which native substitutes for sago are prepared in Japan, the Moluccas, the West Indies, and South Africa. The genus Encephalartos gets its name of Caffre-bread from this fact. The "fossil crows'-nests" of the quarrymen in the Isles of Portland and Purbeck are the stems of Cycadeae.