. The structure and development of mosses and ferns (Archegoniatae). Plant morphology; Mosses; Ferns. VII PTERIDOPHYTA—FILICINE^—OPHIOGLOSSACE^ 253 seen, entirely unbranched. Sections show that here, as in most vascular plants, the growing point of the root is not at the apex, but some distance below and protected by the root-cap. The growth of the root in Ophioglossum can be traced to a single apical cell (Fig. 137), which is of large size, and, like that of the stem, approximately pyramidal in form. While the divi- sions show greater regularity than in the stem, still they are very much less
. The structure and development of mosses and ferns (Archegoniatae). Plant morphology; Mosses; Ferns. VII PTERIDOPHYTA—FILICINE^—OPHIOGLOSSACE^ 253 seen, entirely unbranched. Sections show that here, as in most vascular plants, the growing point of the root is not at the apex, but some distance below and protected by the root-cap. The growth of the root in Ophioglossum can be traced to a single apical cell (Fig. 137), which is of large size, and, like that of the stem, approximately pyramidal in form. While the divi- sions show greater regularity than in the stem, still they are very much less so than in the leptosporangiate Ferns. Seg- ments are cut ofif not only from the lateral faces of the apical cell, but also from its outer face. These outer segments help to form the root-cap, which, however, is not derived exclusively. Fig, tiy.^ophioglossum pendulum. A, Longitudinal; B, transverse sections of the root apex, X21S. from these, but in part also from the outer cells of the lateral segments. Each of the latter is first divided by a nearly ver- tical wall, perpendicular to its broad faces, into two "sextant cells," but beyond this no regularity could be discovered in the order of division in the segments, and the tissue at the growing point, especially in longitudinal section, presents a very con- fused arrangement of the cells. A little lower down two regions are discernible, a central cylinder (plerome), whose limits are not very clearly defined, and the periblem or cortex, A definite epidermis is not distinguishable. The first permanent tissue in the plerome cylinder or stele, which is elliptical in section, arises in the form of small tracheids. 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 Campbell, Douglas Houghton, 1859-1953. New York, The Macmillan Company;
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