. Elements of plant anatomy;. Botany -- Anatomy. ANATOMY OF THE CELL. 15 m the new material is added in such a way that the completed wall is nearly uniform in thickness. On a cross-section through such a cell the limiting siu'faces of the wall appear bounded by straight lines. (Fig. 8.) In the second class the walls are thickened irregularly, the new material being added only to certain portions, leaving thin places through which the liquid contents may pass easily and rapidly from cell to cell. This explains the use of the terms "finer" and "coarser structure" of cell wal
. Elements of plant anatomy;. Botany -- Anatomy. ANATOMY OF THE CELL. 15 m the new material is added in such a way that the completed wall is nearly uniform in thickness. On a cross-section through such a cell the limiting siu'faces of the wall appear bounded by straight lines. (Fig. 8.) In the second class the walls are thickened irregularly, the new material being added only to certain portions, leaving thin places through which the liquid contents may pass easily and rapidly from cell to cell. This explains the use of the terms "finer" and "coarser structure" of cell wall. By "finer structure" is meant ^ stratification or stria- tion or both. " Coarser structure" refers to the more evident sculptur- ing seen on the walls of the latter class. In reference to its direction, growth in thickness may be either centripetal — toward the centre of the cell — or centrifugal — from the centre. In the latter case it must occur on that part of the wall not in connection with the protoplasm. It is evident that centrifugal growth, in this sense, can occur only in cells originally separ- ated from each other, and in those first connected by common walls which have later become partially separated by the division or splitting of their walls. The best example of centrifugal thickening of separate cells is the pollen grain, the outer surface of whose walls is often covered with projections of various forms. Among cells still partly united, examples occur where parts of certain cells of a tissue grow out into neighboring intercellular Fig. 8. Cross section through the wood of Abies pectinata. T T tracheitis, J year's ring, H fall growth, F spring growth, t bordered pore, M medullary ray, m middle lamella, x 300. — (Wiesner.). 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 th
Size: 1904px × 1313px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectbotanya, bookyear1895
