OSMOSE IN CELLS 



179 



in the excentric spirally arranged walls of sclerenchymatous cells 

 with narrow lumina (Fig. 86). l 



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, 



FIG. 86. I, 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 rise to torsional 

 movements. X about 75. After Mur- 

 bach. 



water will be withdrawn from the 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 PfefTer mentions 

 that Aspergillus, under such circumstances, sets up a pressure of 

 1 60 atmospheres (see appendix). 



1 Murbach, L Note on the mechanics of the seed-burying awns of the Stipa 

 Avicenacea. Bot. Gazette. 30 : 113. 1900. 



Remer, W. Beitrage zur Anatomic und Mechanik tordirenden Grannen bei 

 Gramineen, nebst Beobachtungen ueber den biologischer Werthe derselben. Bres- 

 lau. 1900. 



