. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. EMBRYOLOGY 649 absent as a matter of fact in many of the Simplices in their mature state, and apparently from all Ferns in the first condition of the seedling. The vascular structure thus held to be primitive and typical for Ferns is that characteristic of strobiloid plants, and it seems reasonable to read the anatomical data as indicating that the Ferns also are essentially strobiloid, but have progressed to a condition of megaphylly, while the' anatomical characters that ultimately accompany that ha
. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. EMBRYOLOGY 649 absent as a matter of fact in many of the Simplices in their mature state, and apparently from all Ferns in the first condition of the seedling. The vascular structure thus held to be primitive and typical for Ferns is that characteristic of strobiloid plants, and it seems reasonable to read the anatomical data as indicating that the Ferns also are essentially strobiloid, but have progressed to a condition of megaphylly, while the' anatomical characters that ultimately accompany that habit lagged behind in the several evolutionary series, and only become apparent in the later representatives of each. Embryology. The primary embryology of Ferns shows so nearly a dead level of uniformity that it has not seemed necessary to describe the details for the successive families. There are, however, two distinct types: that of. Transverse sections through growing point of root in Osmundaceae. A = Osmunda regalis; the section shows a three-sided initial (jtr), but the segments are not regular. -5=shows transverse section immediately below the root-cap; three initials (x, x) are present; the dotted line is the cell-division in the root-cap, seen on focussing deeply into the hand-cut section ; this shows that the section has traversed the initials and is not below them. C= Todea bar&ara, showing a very regular meristem of the root, with four initials (x, x). X 144. the Marattiaceae, and that of the main series of the Leptosporangiate Ferns, and these must be compared. The most obvious difference lies in the fact that the seedling of the Marattiaceae perforates the prothallus, and emerges with an upright axis through its upper surface (see Fig. 292, p. 527): that of the Leptosporangiate series emerges on the lower surface, and the axis is at first prone (see Figs. 14, 15, pp. 30, 31). This difference may be referred back to the first segmentation of the zygote, and app
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