. Fossil plants : for students of botany and geology . Paleobotany. 470 BENNBTTITAIiES [ Fig. 572. Williamsoniella coronata. Apical disc with megasporophylls and in- terseminal scales at the base. (After Thomas; X 3.) flower. Tte corona is surraounted by a small conical elevation wtich represents the apex of the fertile axis. An apical view of an unexpanded flower is shown in fig. 571, B; the tips of 12 sporophylls are closely pressed against the corona which probably consists in part at least of fused inter- seminal scales. The microsporophylls were shed after the dehiscence of the synang
. Fossil plants : for students of botany and geology . Paleobotany. 470 BENNBTTITAIiES [ Fig. 572. Williamsoniella coronata. Apical disc with megasporophylls and in- terseminal scales at the base. (After Thomas; X 3.) flower. Tte corona is surraounted by a small conical elevation wtich represents the apex of the fertile axis. An apical view of an unexpanded flower is shown in fig. 571, B; the tips of 12 sporophylls are closely pressed against the corona which probably consists in part at least of fused inter- seminal scales. The microsporophylls were shed after the dehiscence of the synangia. Bach sporophyll is flattened on the sides and thicker on the curved outer edge; the synangia, usually in two rows of three, are borne on the sloping sides (figs. 569,570). The surface of a micro- sporophyll is covered with small rounded projections which produce a characteristic appearance. The form of a microsporophyll in section is shown in fig. 570: the synangia are similar in shape to those of Cycadeoidea and Williamsonia {cf. figs. 531, 549, etc.) but there are no external indications of septa like those seen in some other types. On macerating some specimens it was found that the spores occur in about 20 groups. The circular or elliptical spores are 0-02 mm. in diameter. The walls of the epidermal cells of the micro- sporophylls are straight: the stomata, which show the features characteristic of the Bennettitales, agree closely with those of Taenopteris vittata. The interseminal scales associated with the ovules and covering the pyriform axis above the microsporophylls are more or less flattened and hexagonal and the micropylar tubes often project far beyond the scales. Each micropyle-tube is surrounded by 5—6 interseminal scales {cf. fig. 564). The ovules differ from those of Cycadeoidea Gibsoniana in the absence of a distinct pedicel and agree with the corresponding organs of Williamsonia scotica^ In the absence of epidermal papillae the micropylar tubes resemble
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishercambr, bookyear1898
