. Elements of plant biology. Plant physiology. 282 TISSUE ELEMENTS OF SEED PLANTS Both these types are formed in tissue which is stilV elongating, and the stretching of the thin cell wa^l separates the coils of the spiral or the annuli, as the case may be (Fig. 45, B—G). (c) Pitted tracheids have general thickening of the cell wall, but with numerous pits often set so close together (Fig. 45, J) that only ribs of thickening are formed between them. The pits are generally bordered, often with greatly overhanging walls (Fig. 45,1). When the pits are elongated and horizontal in direction, as seen
. Elements of plant biology. Plant physiology. 282 TISSUE ELEMENTS OF SEED PLANTS Both these types are formed in tissue which is stilV elongating, and the stretching of the thin cell wa^l separates the coils of the spiral or the annuli, as the case may be (Fig. 45, B—G). (c) Pitted tracheids have general thickening of the cell wall, but with numerous pits often set so close together (Fig. 45, J) that only ribs of thickening are formed between them. The pits are generally bordered, often with greatly overhanging walls (Fig. 45,1). When the pits are elongated and horizontal in direction, as seen in surface view, running across one face of a poly-. FlG. 46.—Part of a spiral tracheid very highly magnified and seen in longitudinal section, showing attachment of the spiral thickening band to the thin wall. gonal tracheid, so that there are horizontal bars of thickening between successive pits, like the rungs of a ladder, the tracheid is called scalariform (Fig. 45, H). When the pits are angular and variable in outline, so that there is a network of thickening between them, we have the reticulate type (K). The pits are, however,, very often circular, oval or polygonal in outline and very closely set (J). A vessel has its walls lignified and thickened just like a tracheid, but it consists of a row or chain of. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Tansley, Arthur George, 1871-. London, George Allen & Unwin Ltd. ; New York, Dodd, Mead & Co
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectplantph, bookyear1922
