. Comparative anatomy of the vegetative organs of the phanerogams and ferns. Plant anatomy; Phanerogams; Ferns. SIEVE-TUBES OF CRFPTOGAMS. FIG. 78. — Encephalartos pungens. Bast of an old stem. Part of the radial wall of a sieve-tube (375). plates are not callous. Their pores, as far as they can be recognised, are very narrow and round; and in INIarsilia, according to Russow, very numerous on one plate; in the cases investigated by me (Pteris aquilina, Cyathea, Alsophila spec, Osmunda) they are less numerous, and relatively far distant from one another. The wall of the tubes is thin at the sie
. Comparative anatomy of the vegetative organs of the phanerogams and ferns. Plant anatomy; Phanerogams; Ferns. SIEVE-TUBES OF CRFPTOGAMS. FIG. 78. — Encephalartos pungens. Bast of an old stem. Part of the radial wall of a sieve-tube (375). plates are not callous. Their pores, as far as they can be recognised, are very narrow and round; and in INIarsilia, according to Russow, very numerous on one plate; in the cases investigated by me (Pteris aquilina, Cyathea, Alsophila spec, Osmunda) they are less numerous, and relatively far distant from one another. The wall of the tubes is thin at the sieve-plates; the rest of it is strongly thickened, stratified, and soft, and apparently swells in water. These tubes contain a quantity of watery fluid, and a thin peripheral layer, coloured yellow by iodine, which contains throughout, and especially at the ends of the members, and on the lateral sieve-plates, numerous very small granules which adhere closely to the wall. In dried-up tubes the ends are also found filled with a homo- geneous brown mass. These granules are not starch: they turn a deep yellow with preparations of iodine: maceration in dilute solution of potash destroys them only partially even after many days. Their dense aggregation and their tenacious hold on the sieve-plates usually prevents a clear decision on. the permeability of the pores: but I believe that I have clearly seen in thin longitudinal sections in Pteris aquilina that the granules of con- tiguous sieve-tubes are connected by thin filamentous processes which tra- verse the transverse pores (Fig. 79, c). The tubes are not inferior in v/idth to the medium and thicker tubes of the Gymnosperms. The length of the single members is considerable, in the cases investigated (Pteris aquilina, Cy- atheacese) it is 1-31"^™. In the Mar- silias they attain, according to Russow, the length of one whole internode, that is, of several centimetres, a statement which may have its origin in the ease with whic
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Keywords: ., bookcentury1800, bookdecad, booksubjectplantanatomy, bookyear1884
