. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. 400 SPHENOPHYLLALES.—A. Sl'HENOPHYLEEAE early, so that the unaltered primary state is seen only in small twigs. Here a protostelic structure is seen, without any pith or conjunctive parenchyma. The primary \ylem is of triangular form, the groups of protoxylem, either single or double, being at the projecting angles; or the angles may be duplicated, and a hexarch form be attained. The vascular system is strictly cauline : it passes through the nodes without any appreciable change of structure, a point
. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. 400 SPHENOPHYLLALES.—A. Sl'HENOPHYLEEAE early, so that the unaltered primary state is seen only in small twigs. Here a protostelic structure is seen, without any pith or conjunctive parenchyma. The primary \ylem is of triangular form, the groups of protoxylem, either single or double, being at the projecting angles; or the angles may be duplicated, and a hexarch form be attained. The vascular system is strictly cauline : it passes through the nodes without any appreciable change of structure, a point of interest for comparison with the Equisetal structure as interpreted by ( A peculiarity of some importance for further comparison is shown in the primary wood. 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 resemble the original Bower, F. O. (Frederick Orpen), 1855-1948. London, Macmillan and Co. , Ltd.
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