Chapter VII — 85 — Osmotic Quantities of Cells 



greater than normal (Currier, 1943). Martens (1931) demonstrated a 

 marked extensibility in staminal hairs of Tradescantia virginica, amounting 

 to increases in length of 100 to 150 per cent for cells freed of their cuticle. 

 The review by Heyn (1940) and Ursprung's monograph (1938) may be 

 consulted for a discussion of plastic and elastic stretching of cell walls. 



Similarly it seems certain from the work of Delf (1916) and Pring- 

 SHEiM (1931) that plasmolysis in strongly hypertonic solutions causes 

 plastic shrinking of cell walls, tending to increase somewhat the DOg value 

 in comparison with Og values. 



Gasser (1942) was unable to demonstrate adhesion pressure in several 

 plants which he investigated. Bennet-Clark, Greenwood, and Barker 

 (1936) definitely oppose the idea that it may invalidate plasmolytic meas- 

 urements, at least for the plant material used {see Table 30). They give 

 the following reasons: "the magnitude of the difference [between cryo- 

 scopic and plasmolytic measurements of OP] is too great; deformation of 

 the cell wall such as is demanded by the adhesion view is not observed ; it 

 should be impossible to observe cells in equilibrium in the condition of limit- 

 ing plasmolysis, which in actual fact are seen in large numbers." 



Sufficient evidence has been reported to indicate that adhesion does 

 occur but it probably has not been a serious factor in most of the measure- 

 ments made by the plasmolytic method. Actually the nature of the asso- 

 ciation between the cell wall and cytoplasm is not well understood. If, as 

 has been suggested, the wall is a living part of the cell, there is good reason 

 to postulate an intimate structural bond between the two. Balazs (1943), 

 investigating epidermal cells, believes that the fine threads connecting the 

 separated protoplast with the wall ( Chodat-Hecht filaments) are derived 

 from the wall and not from the protoplast. Careful observation of plas- 

 molysed onion bulb cells on the other hand indicates that these threads may 

 be continuous with the plasmodesmata of pits and hence have an intimate 

 relation with the protoplasmic connections normally present. 



L. and M. Brauner (1943&) believe that there is no general explana- 

 tion for the adhesion of protoplasm to walls, since various conditions may 

 act to produce different behavior in the same material. 



Of the various kinds of plants to which plasmolytic methods have been 

 applied, the marine algae {Phaeophyceae, Rhodophyceae) have perhaps 

 yielded the most unreliable data (Kotte, 1915; Hofler, 1930, 1931; 

 Hoffman, 1932; Bunning, 1935). The trouble appears to lie in a rela- 

 tively high permeability towards the plasmolyzing solute, in marked swell- 

 ing of the wall and protoplasm, depending on the solution employed, in 

 volume changes that are difficult to measure due to irregular shapes of cells, 

 and in a strong adhesion of the protoplasm to the wall. According to de 

 Zeeuw (1939) the wall swells as plasmolysis is approached due both to 

 release of turgor pressure, and to the imbibing of the relatively pure water 

 passing through from the vacuole. The relationship may be more than 

 adhesion; Bunning (1935) states that the protoplasm may permeate from 

 one third to one half of the wall in Callithamnion roseum. It is therefore 

 not surprising that plasmolysis is injurious to these plants. 



Plasmolytic Method — Experimental Procedure: — A recommended procedure for 

 determining the limiting plasmolysis value Og of a tissue is as follows : sections of 

 tissue are cut to such a thickness that one to four layers of intact cells remain. They 

 are quickly distributed among graded, weight molar sucrose solutions, the concentra- 

 tions of which vary by steps of 0.02 to 0.05 M. Infiltration by means of a vacuum 

 pump will shorten the time necessary to attain equilibrium and will reduce optical 



