. Elementary plant physiology. Plant physiology. 54 Elementary Plant Physiology. I additional volume of water taken into the cavity, and the walls are held rigid and firm by the pressure. Living cells are gen- erally in a similar state of turgidity, and the firmness of soft- bodied organs is due almost entirely to the turgidity of the cells. Large plants, such as trees, secure firmness of the trunks and branches by great masses of dead tissues mechanically joined and arranged to secure stiffness (Fig. 31). The walls of some cells are more elastic and stretch farther under the pressure of turgi
. Elementary plant physiology. Plant physiology. 54 Elementary Plant Physiology. I additional volume of water taken into the cavity, and the walls are held rigid and firm by the pressure. Living cells are gen- erally in a similar state of turgidity, and the firmness of soft- bodied organs is due almost entirely to the turgidity of the cells. Large plants, such as trees, secure firmness of the trunks and branches by great masses of dead tissues mechanically joined and arranged to secure stiffness (Fig. 31). The walls of some cells are more elastic and stretch farther under the pressure of turgidity, and the osmotic value of the cell sac varies greatly in differ- ent instances. Inequalities in turgidity of tis- sues fastened to- gether, and joined to dead cells in which turgidity does not exist, gives rise to _ ^ stresses and ten- Fig, 32.—Behavior ox tissues due to tensions, a, positions SlOns DCtween me assumed bytlie Iialvesof aslicetliroughtliecenterof astern; different parts of by diagram of a stem and relative lengtii of pith and wood ^ fV. when separated ; >K,»i,OT,»2,parenchyma. After Hansen. Stems and Other Structures. 49. Tissue tensions.—If the parts of a tent or some similar structure are cut apart, they quickly assume forms and positions quite different from those in which they were bound together under tension. The same may be said of the tissues in a stem. Cut a slice a centimeter in thickness, and 10 cm. in length, from the center of a petiole of rhubarb {Rheum), petiole of Calla, or young stem of elder {Sa??ibucus). Lay flat in a dish. Now divide longitudinally in the middle by a single downward. 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 MacDougal, Daniel Trembly, 1865-1958. New York, London [etc. ] Longmans, Green, and Co.
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