. An introduction to the structure and reproduction of plants. Plant anatomy; Plants. STRUCTURE OF FERN-STEM 293 walled cells having comparatively few contents. Next follow one or two layers of much smaller cells, constituting the so-called phloem-parenchyma (). Immediately rfithin is a conspicuous zone consisting chiefly of large, empty-looking, thin-walled elements, the sieve-tubes (5.), which are often absent towards the ends of the strands, and which are separated from the central xylem by a zone of small-ceUed wood-parenchjma [). The bulk of the xylem consists of large tracheids (
. An introduction to the structure and reproduction of plants. Plant anatomy; Plants. STRUCTURE OF FERN-STEM 293 walled cells having comparatively few contents. Next follow one or two layers of much smaller cells, constituting the so-called phloem-parenchyma (). Immediately rfithin is a conspicuous zone consisting chiefly of large, empty-looking, thin-walled elements, the sieve-tubes (5.), which are often absent towards the ends of the strands, and which are separated from the central xylem by a zone of small-ceUed wood-parenchjma [). The bulk of the xylem consists of large tracheids (Xy.), but near the ends and towards the centre of the strand, small ele- ments, representing the protoxylem (), can usually be recognised. There is generally a small central mass of wood-parenchyma. In longitudinal sections, cut so as to pass radially through a stele (Fig. 161), the sieve- tiihes (s.) appear as elongated structures with tapering ends, and bearing the sieve areas on their sloping radial Fig. 161. -On the left, part of a radial longi- tudinal section through one of the steles of the Bracken-rhizome, e., endodermis ; , ground tissue; p., pericycle ; , phloem- parenchyma ; sieve-tube ; t., tracheid of the metaxylem ; , xylem-parenchyma. On the right, a little of the sclerenchyma (Scl.) in longitudinal section. Under the high power these sieve areas exhibit a rather irregular ladder-like (scalariform) thickening of shining bars, with intervening darker zones exhibiting a fine dotting and bearing a number of highly refractive adhering granules. The longitudinal walls of the metaxylem tracheids [t.) exhibit several rows of closely arranged oblong bordered pits, producing an exceedingly characteristic type of scalariform thickening, whilst the protox5dem tracheids are spirally thickened in the usual way. The number of vascular strands observed in a transverse. Please note that these images are extracted from scanned page images that
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectpl, booksubjectplants
