. Fossil plants : for students of botany and geology . Paleobotany. xxvni] EBPKODUCTIVE SHOOTS 23 aggregated into cones, but in Dioon the strobili are characterised by their more ovoid form and by the looser arrangement of the sporophylls (fig. 386, B), each of which consists of a horizontal stalk expanded distally into a broadly lanceolate upturned end covered with a thick felt of hairs and bearing at its base usually 2, rarely 5—6, ovules on cushion-like swellings. In Dioon spinu- losum the cones may be 50 cm. long. Between the cones of Microcycas, over 90 cm. long, and those of some Zamias,
. Fossil plants : for students of botany and geology . Paleobotany. xxvni] EBPKODUCTIVE SHOOTS 23 aggregated into cones, but in Dioon the strobili are characterised by their more ovoid form and by the looser arrangement of the sporophylls (fig. 386, B), each of which consists of a horizontal stalk expanded distally into a broadly lanceolate upturned end covered with a thick felt of hairs and bearing at its base usually 2, rarely 5—6, ovules on cushion-like swellings. In Dioon spinu- losum the cones may be 50 cm. long. Between the cones of Microcycas, over 90 cm. long, and those of some Zamias, a few centimetres long, there are many intermediate forms. The. Fig. 394. Macrozamia Preissii, megastrobilus and (A) single megasporophyll; a, axis of cone; j), stalk of megasporophyll; «, unripe seeds. (After Eendle.) large strobilus of an Encephalartos reproduced in fig. 393, D, shows the convex ends of the sporophylls with a jagged edge, and in monstrous cones the marginal lobes may be abnormally developed and assume the appearance of pinnae^. Each mega- sporophyll bears two large ovules (fig. 393, B). In certain species of Encephalartos the swollen ends of the sporophylls have a trun- cate centre hke the flattened umbo of some Pines (fig. 392, D). The presence of two divergent spines is a peculiarity of the mega- 1 Thiseltou-Dyer (01); Bot. Mag. 1915, Tab. 8592, 8593. monstrous cones, see Miquel (69), Wieland (02). For instances of. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Seward, A. C. (Albert Charles), 1863-1941. Cambridge : University Press
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