Page:Popular Science Monthly Volume 80.djvu/202

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THE POPULAR SCIENCE MONTHLY

PSM V80 D202 Historical connections of the groups of gymnosperms.png

Historical Connections of the Groups of Gymnosperms: 1, Cycadofilicales; 2, Cordaitales; 3, Bennettitales; 4, Cycadales; 5, Ginkgoales; 6, Coniferales; 7, Gnetales.

chiefly from material obtained from the Coal-measures. Although the two groups are equally ancient, so far as our records go, having been recognized well into the Middle Devonian, it is quite evident from comparative structures that the Cycadofilicales are the more primitive, and presumably the more ancient. Whether they are actually the most ancient seed plants or not, they are at least the most primitive seed plants of which we have any knowledge.

The presence of this great group of primitive seed plants (Cycadofilicales) in the Paleozoic was obscured for many years by the impression that they were ferns. A very large percentage of the Coal-measure