. Carnegie Institution of Washington publication. THE YOUNG SPOROPHYTE 73 be said to be concentric, it nevertheless approaches closely the collateral type of the other Ophioglossaceae. The fusion of the two leaf traces to form the single axial bundle in the basal part of the internode is very much like that found in the young sporophyte of Bo- trychium (fig. 40, D, F). The endodermis of the two bundles becomes continuous and there may be seen intermediate stages of a single bundle, oval in section, but with two conspicuous xylems, separated by the mass of large, thin-walled tissue which gradua
. Carnegie Institution of Washington publication. THE YOUNG SPOROPHYTE 73 be said to be concentric, it nevertheless approaches closely the collateral type of the other Ophioglossaceae. The fusion of the two leaf traces to form the single axial bundle in the basal part of the internode is very much like that found in the young sporophyte of Bo- trychium (fig. 40, D, F). The endodermis of the two bundles becomes continuous and there may be seen intermediate stages of a single bundle, oval in section, but with two conspicuous xylems, separated by the mass of large, thin-walled tissue which gradually disappears as the bundle is followed downward; and finally, in the lower part of the internode, the section of the stele appears quite circular, the center being occupied by the solid xylem formed by the complete coalescence of the xylems of the fused leaf traces (fig. 49, /). The arrangement of the phloem, pericycle, and endodermis is the same as in the single leaf trace f y^yr'^Vy i '""' in the upper region of the ^VxhSW; internode. The base of the stip- ular sheath can be fol- lowed downward to about the level where the two leaf traces begin to coal- esce. Its anterior free portion, between which and the internode is a narrow slit, finally be- comes quite free and its section is visible as an oblong mass of cells lying quite separate from the section of the internode. Longitudinal sections of a somewhat older sporophyte are shown in fig. 48, A, B; the third leaf is pretty well developed, with the stipular sheath completely overarching the stem apex and the fourth leaf, which already is conspicuous. The third leaf is still completely covered by the large stipular sheath of the second leaf, which apparently forms a closed cavity; but an examination of the adjoining sections showed that the ante- rior margin of the, sheath is quite free in front and that there is a narrow cleft between it and the internode. The real nature of the sheath and its relation to the lea
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Keywords: ., bookauthorcarnegie, bookcentury1900, bookdecade1910, bookyear1911
