. The structure and development of mosses and ferns (Archegoniatae). asm remains in them. Faint elongatedtransverse pits become evident, and the spaces between theserapidly thicken at the expense of the cell contents until all theprotoplasm is used up. The thickened bars between the pitsgive the characteristic ladder-like appearance to the older IX FILICINE^ LEPTOSPORANGIAT^ 331 tracheid (Fig. 184, B). In cross-section these bars are nearlyrhomboidal, and give the famihar beaded appearance to sectionsof the tracheid wall. Sieve-tubes of very characteristic form are found in thebundles of all t
. The structure and development of mosses and ferns (Archegoniatae). asm remains in them. Faint elongatedtransverse pits become evident, and the spaces between theserapidly thicken at the expense of the cell contents until all theprotoplasm is used up. The thickened bars between the pitsgive the characteristic ladder-like appearance to the older IX FILICINE^ LEPTOSPORANGIAT^ 331 tracheid (Fig. 184, B). In cross-section these bars are nearlyrhomboidal, and give the famihar beaded appearance to sectionsof the tracheid wall. Sieve-tubes of very characteristic form are found in thebundles of all the Polypodiaceae. In O. striithiopteris theyoccupy an irregular area at each end of the bundle. Theirdifferentiation begins shortly after that of the large scalariformtracheids, and in some respects resembles it. The procambiumcells from which they arise are uniform in diameter, and havesquarer ends than the young tracheids. Their contents aremore colourless and finely granular than those of the tracheids,and the nucleus not so evident. The formation of the sieve-. en
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Keywords: ., bookauthorcampbelldouglashought, bookcentury1900, bookdecade1910
