. Morphology of gymnosperms. Gymnosperms; Plant morphology. CYCADALES 117 young staminate cones of Zamia floridana and Chamberlain (63) described spermatogenesis in Dioon edule. The sporophylls first appear as minute papillae, giving the young cone a wavy contour as seen in longitudinal sections (figs. 96, 97). According to Miss Smith, there is in Zamia a single archesporial cell, the first division of which may be either periclinal or anticlinal, but in any case primary wall cells and primary sporogenous cells are soon formed (figs. 101-104). In Stangeria Lang (22) first recognized the arches
. Morphology of gymnosperms. Gymnosperms; Plant morphology. CYCADALES 117 young staminate cones of Zamia floridana and Chamberlain (63) described spermatogenesis in Dioon edule. The sporophylls first appear as minute papillae, giving the young cone a wavy contour as seen in longitudinal sections (figs. 96, 97). According to Miss Smith, there is in Zamia a single archesporial cell, the first division of which may be either periclinal or anticlinal, but in any case primary wall cells and primary sporogenous cells are soon formed (figs. 101-104). In Stangeria Lang (22) first recognized the archesporium as a hypodermal plate of four cells (figs. 105-109). By comparing these figures with those of Miss Smith, it is evident. Fig. 100.—Microsporophylls of cycads: A, Cycas circinalis {a, entire sporophyll, showing sporangia on under surface; 6, four groups of sporangia; c, same as 6 after the pollen has been shed); B, Zamia integrifoUa (a, entire sporophyll; b, c, clusters of sporangia).—Ab, Ac, after Bltjme; the rest after Richard; the whole figure taken from Engler and Prantl's Natilrlichen Pflanzenfamilien. that Stangeria develops like Zamia, the hypodermal plate having come from a single cell. The later stages are essentially the same in both accounts. A sporangium wall several cells in thickness is developed, and also a large mass of sporogenous tissue, from the periphery of which the tapetum is differentiated. While the origin of the tapetum was not studied in Dioon, fig. no would indicate that it is more probably derived from the wall cells. The resemblance of the cycadean sporangia to those of the marattiaceous fern Angiopteris is quite striking, the principal difference being the comparatively scanty development of the tapetum in the cycad (fig. in). As the spores mature, the epidermal layer of the sporangium becomes thick-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and
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