Nature and development of plants . with stems 12 to 60 feet vascular bundles are collateral and arranged around a larse 322 THE CYCADALES pith as noted in Botrychinm. A slight enlargement of the stemis brought about owing to the weak growth of the cambium ofthese bundles, but the principal increase is effected by the for-mation of new bundles outside of those first formed. Concentricbundles also occur in the leaves and portions of the stem ofcertain species. The foliage leaves are large and leathery andform a rosette, alternating with scale leaves, at the apex of thestem. The bases of
Nature and development of plants . with stems 12 to 60 feet vascular bundles are collateral and arranged around a larse 322 THE CYCADALES pith as noted in Botrychinm. A slight enlargement of the stemis brought about owing to the weak growth of the cambium ofthese bundles, but the principal increase is effected by the for-mation of new bundles outside of those first formed. Concentricbundles also occur in the leaves and portions of the stem ofcertain species. The foliage leaves are large and leathery andform a rosette, alternating with scale leaves, at the apex of thestem. The bases of these leaves form an armor-like plate overthe surface of the stems. In certain genera, the young leavesare coiled as in the ferns. (a) The Sporophylls and Sporangia of the Cycads.—Thesporangia are borne on more or less modified leaves arrangedin large terminal strobili and either scattered over the sporophyllor sometimes arranged in groups suggestive of the sori of theferns, in some forms even showing a rudimentary annulus. In. FlG. 244. Zamia, a cycad common in southern Florida, with strohilus ofmegasporophvlls.—H. O. Hanson. origin and development, they are strikingly like the lower is a considerable variation in the form of the sporophyllsand the distribution of the sporangia. For example, in Cycas,the megasporophvlls are loosely associated and only slightly DEVELOPMENT OF PLANTS 323 modified, the sporangia being developed on their margins (, 3^). The microsporophylls are small and more compactlyarranged, the sporangia being associated in sori on the lower
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