Title: The structure and development of mosses and ferns (Archegoniatae) Year: 1918 (1910s) Authors: Campbell, Douglas Houghton, 1859-1953 Subjects: Publisher: New York, Macmillan

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Text Appearing Before Image: X 5; ^, the sorus. initial cell, but only a small part of the segments give rise toleaves, which are arranged in two ranks. The stem in all investigated Hymenophyllacese is mono-stelic, and one leaf-trace passes to each leaf. The cortex isusually largely made up of sclerenchyma, especially the innercortex. In Hymenophyllum recurvum (Fig. 220), the axialvascular bundle is strictly concentric. Occupying the centreis a curved band of tracheary tissue, the small central tracheidsbeing the protoxylem. Around the xylem is a continuous zone X THE HOMOSPOROVS LEPTOSPORANGIAT^ 379 of phloem, separated from the endodermis by a broad pericycle.In other species of HymenopJiylliim, Boodle (i) found a dif-ferent arrangement of the xylem and phloem. In some cases,e g., H. scabnim, there are two xylem plates, with the proto-xylem elements in the conjunctive tissues between them. In Trichomanes there is also a good deal of variation. Fig.220, B, shows the structure in T. venosiim, a small species from

Text Appearing After Image: Fig. 220.—A, Section of the rhizome of Hymenophyllum recurvum, X about 40; B,rhizome of Trichomanes venosum, X about 75; C, stele of B, more highly mag-nified; D, root of Hymenophyllum recurvum, X about 75; E, stele of the rootmore highly magnified. Australia and New Zealand. The structure of the stem dif-fers from that of Hymenophyllum recurvum, mainly in itsgreater delicacy. The sclerenchyma of the cortical region isless developed, and the concentric axial cylinder correspondingto its much smaller size has both the xylem and phloem reducedin amount. In the stouter species, like T. radicans, the amount of wood 38o MOSSES AND FERNS chap. is much greater. According to Boodle (1. c. Fig. 24), thereare two or three protoxylems, accompanied by parenchymacells, surrounded by a massive ring of large tracheids. Thereis an approach in this species, and still more in T. reniforme,to the form characteristic of Hymenophyllum scabrum and itsallies. In the small species, T. muscoides, apparently

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