. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. GENERAL MORPHOLOGY 373 The leaves themselves were usually simple, as in Equisetum, though of greater dimensions, and accordingly more effective as assimilating organs ; but among the earliest forms, such as Asterocalamites (Schimper), from the Culm, the leaves were branched in repeated dichotomies (Fig. 199). In the very early Pseudobornia, from the upper Devonian of Bear Island,1 the foliage was forked in a fan-like fashion, and of considerable dimensions. Another feature, in which certain of the ear
. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. GENERAL MORPHOLOGY 373 The leaves themselves were usually simple, as in Equisetum, though of greater dimensions, and accordingly more effective as assimilating organs ; but among the earliest forms, such as Asterocalamites (Schimper), from the Culm, the leaves were branched in repeated dichotomies (Fig. 199). In the very early Pseudobornia, from the upper Devonian of Bear Island,1 the foliage was forked in a fan-like fashion, and of considerable dimensions. Another feature, in which certain of the earliest forms differed from the later, was in the fact that the members of successive whorls were super- posed, and did not alternate ( Asterocalamites). Such forms have been Equisetum pratense, Ehrh. Shoots showing recurrent whorls of sporangiophores and of bracts. (After Milde.). Phyllotheca. Zigno. A, Ph. equisetifo-mis from Rovere di Velo, near Verona. B, inflores- cence from Siberia, placed by Schmalhausen with Phyllotheca. (After Solms.) associated by Potonie as a family of " ; The facts would seem to indicate then a primitive construction of the Equisetoid shoot as having relatively large whorled and superposed leaves, effective as assimilating foliage: these were also separate from one another, and liable to bifurcation. The condition, as seen in the present Equisetum. might be understood as attained by reduction of the coalescent and simple leaves, which became also alternate instead of superposed, while the assimilatory function was relegated almost entirely to the axis. But there is no certain proof that the actual evolution of Equisetum itself was along such a line as this. 'Nathovst, ; Foss. Flora d. Folarlander, i., Lief. 3, Taf. 7, s-. 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 r
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