. The structure and development of mosses and ferns (Archegoniatae). Plant morphology; Mosses; Ferns. VI. THE BRYALES 191 appendages of the stem. The inner cells of the segments by repeated longitudinal and transverse divisions form all the tis- sues of the axis. The second division wall in the segment, like that in Sphagnum, is at right angles to the first, but in Ambly- stegium it extends the whole breadth of the segment. By this division the outer of the two primary cells of the segment is divided into an upper cell, from which the leaf develops, and a lower one from which the outer part of
. The structure and development of mosses and ferns (Archegoniatae). Plant morphology; Mosses; Ferns. VI. THE BRYALES 191 appendages of the stem. The inner cells of the segments by repeated longitudinal and transverse divisions form all the tis- sues of the axis. The second division wall in the segment, like that in Sphagnum, is at right angles to the first, but in Ambly- stegium it extends the whole breadth of the segment. By this division the outer of the two primary cells of the segment is divided into an upper cell, from which the leaf develops, and a lower one from which the outer part of the stem and the buds are formed. The leaves grow from a two-sided apical cell. Fig. 98.—Amblystegium riparium, var. Huitans. A, Median longitudinal section of a strong shoot; x, apical cell; x*, initial of a lateral branch, X250; B, transverse section through the apex, X2S0; C, similar section through a young branch, XS""- (Fig. 99), as indeed they seem to do in all Mosses, and the divisions proceed with great rapidity and the young leaves quickly grow beyond and surround the growing point. In Amblystegium, as in all the typical Bryales, the leaf has a well- developed midrib. The formation of this begins while the leaf is very young and proceeds from the base. In the middle row of cells (Fig. 99, C), a wall first arises parallel to the surface of the leaf, and this is followed by a wall in the cell on the lower side of the leaf (Fig. 99, D). By further divisions in all the. 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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