T. C. Br oyer 189 



tissue (52, 81, 82), epidermal tissue (24, 34), whole (intact) plants (5"?), 

 and roots (38, 66). Such results have been reviewed by Brooks and 

 Brooks (9) and Stiles (So), and in annual reports (86) entitled "Perme- 

 ability" or "Mineral Nutrition of Plants." 



The condition of permeability in the strict sense is an important one, 

 for, with a surface limiting entry of materials, the broader aspect of 

 inorganic solute and/or water absorption may be controlled or re- 

 stricted. In the earlier literature the term permeability was broadly used. 



TABLE I 

 Differential Accumulation of Ions in Halicystis, Nitella, and Chara 



Halicystis 

 Sea Osier- Pond Brackish 



Ion Water Oralis houtii Water Nitella Water Chara 



M M M M X io 3 M X io 3 M X io 3 M X io 3 



CI 0.52 0.55 0.60 0.90 90.8 73 o 225.0 



Na 0.50 0.22 0.56 0.22 10.0 60.0 142.0 



K 0.01 0.32 0.006 0.05 54.3 1.4 88.0 



Note: Comparison is made of the concentrations of the principal ions between the vacuolar 

 sap and the external bathing medium under natural conditions. 



However, with advance of research, more specific terminology has been 

 applied. Some of these terms have been defined in recent reviews (10, 

 11) and as such will be generally used in this treatise. 



It has been recognized for some time that limiting surfaces or mem- 

 branes are involved where studies on absorption are concerned with 

 living cells and tissues. Several theories have been proposed for the dif- 

 ferential permeability of living surfaces relative to penetration of solutes. 

 Studies on the entry of dyes and relatively nonpolar compounds led to 

 the lipoidal theory propounded by Overton (55). This is a solution 

 hypothesis of permeability, assuming as it does that the penetration of 

 different substances runs parallel with their solubility in lipoidal sub- 

 stances of which the limiting surfaces are supposed to be composed. 

 However, there are compounds which are soluble in lipoidal substances, 

 and yet have been found not to enter living cells with significant rapid- 



