. Practical text-book of plant physiology. Plant physiology. OSMOSE IN CELLS 179. in the excentric spirally arranged walls of sclerenchymatous cells with narrow lumina (Fig. 86).: 248. Osmose in Cells. The cell is an osmotic system of mem- branes, each with its own specific permeability;, in addition the outer and most permeable of these, the wall, is rigid and pos- sesses great structural strength. When the plasmatic membranes become filled with solutions and press against the wall, it is stretched only slightly and as- sumes a state of great rigidity, and the cell in such condition of disten
. Practical text-book of plant physiology. Plant physiology. OSMOSE IN CELLS 179. in the excentric spirally arranged walls of sclerenchymatous cells with narrow lumina (Fig. 86).: 248. Osmose in Cells. The cell is an osmotic system of mem- branes, each with its own specific permeability;, in addition the outer and most permeable of these, the wall, is rigid and pos- sesses great structural strength. When the plasmatic membranes become filled with solutions and press against the wall, it is stretched only slightly and as- sumes a state of great rigidity, and the cell in such condition of distention is said to be in a state of turgidity. If a turgid cell is immersed in a solution to which the outer wall is permeable, and which has a higher isotonic coefficient than the solution held in the plasmatic membrane, water will be withdrawn from the plasma, and it will shrink away from the wall, and is said to be plasmolyzed. On the other hand, if organisms accustomed to living in concentrated solutions are placed in pure water, so much of this substance may be taken up that a pressure sufficient to rend the wall may be generated. This may be seen in some pollen grains, and Pfeffer mentions that Aspergillus, under such circumstances, sets up a pressure of 160 atmospheres (see appendix). 1 Murbach, L Note on the mechanics of the seed-burying awns of the Stipa Avicenacca. Bot. Gazette. 30: 113. 1900. Reiner, W. Beitrage zur Anatomie und Mechanik tordirenden Grannen bei Gramineen, nebst Beobachtungen ueber den biologischer Werthe derselben. Bres- lau. 1900. Fig. 86. 1, cross section of half of the axis of an awn of Stipa Avicenacea, showing disposition of the mechanical cells. 2, portion of a single cell seen in longitudinal section, in an air-dry condi- tion, showing spiral arrangement of the wall. 3, optical section of a portion of 2 taken from x in I. 4, portion of sim- ilar cell after treatment with macerating fluid. 5, diagram showing the resultant of forces that may give r
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