Grafts etal. —84— Water in Plants 



wall. Walls exhibit, in varying degree, both elasticity and plasticity, the 

 latter defined as "the ability to undergo permanent irreversible changes in 

 size and shape" (Heyn, 1940). Cells whose walls exhibit excessive plastic- 

 ity during severe plasmolysis or deplasmolysis are not suitable material for 

 this type of experiment. 



Table 21. — Measurement of adhesion pressure in Beta vulgaris root 

 (data of BuHMANN, 1935) : — 



Plasmolysis (POg) Deplasmolysis (DOg) Adhesion pressure 



atm. atm. atm. 



19.61 16.35 3.26 



18.13 15.64 2.49 



18.87 17.42 1.45 



18.13 17.06 1.07 



Such plastic stretching has been observed in beetroot tissue by Pring- 

 SHEiM (1931). Some representative data are presented in Table 22. 

 Stretching would be expected to aflfect measurements of Og. Sections of 

 beet tissue soaked in tap water for an hour gave an Og value as much as 



Table 22. — Longitudinal strips of beetroot (Futterriibe) 14 cm. long, soaked for 



various times in water, then overnight in 0.5 M KNOs- Change in length is expressed 



in per cent of initial length (data of Pringsheim, 1931) : — 



5.7 atmospheres less than sections not soaked in this way. Table 23 shows 

 these results. Unless otherwise stated, the symbol Og refers to the osmotic 

 pressure at limiting plasmolysis approached from the normal state. This 

 is interpreted as due to plastic stretching of the cell wall, causing plasmoly- 

 sis to set in at a greater than normal cell volume. Such an interpretation 

 neglects any error caused by loss of vacuolar solutes during soaking. Com- 

 plete absence of anthocyanin in the tap water is taken for evidence that no 

 injury was present. Presumably loss of solutes was slight, if present at all 

 during the one-hour period. 



Table 23. — Effect of zvater saturation on Og values (Currier, 1944a) : — 



Og (usual method) Og (water saturated) Difference 



ATM. ATM. ATM. 



Volume change studies on isolated mesophyll cells of Sedum nicaense 

 have shown that considerable plastic stretching of these cells occurs upon 

 soaking. Incipient plasmolysis of such cells often occurs at cell volumes 



