THE CELL. 9 



depend upon this plasmic impenneabilitj. This term should be 

 used with caution. There certainly is no subjective choice. 

 "Whether a given substance is taken up by the plant depends upon 

 whether it is of use or not. The unequal utilization of certain sub- 

 stances by different plants depends upon inherent peculiarities of the 

 plants. For example, of two plants growing in the same soil one 

 will take up much and the other little silica (SiO,), the one much 

 and the other little calcium carbonate, and deposit it in the cell- 

 walls. The above-mentioned behavior of plasm toward poison- 

 ous solutions is quite different and might in a certain sense justify 

 the term choice. It is, however, strictly speaking only the reaction 

 of the living plasm to chemical stimuli. 



For the investigations concerning plasmolysis we are indebted 

 to several authors, Nageli, Pringsheim, Pfeffer, and more recently 

 Hugo de Yries. To the last-mentioned investigator we are indebted 

 for a very important treatise entitled the '• Analysis of the Turgor 

 Force." ' This analysis was made by determining the so-called "iso- 

 tonic coefficients." I will select only the following statements 

 from the work of de Yries. The iveakest solution (expressed in 

 gram-molecules, not per cents) of potassium nitrate (Kl^^Og) M'hich 

 is just capable of inducing plasmolysis within a cell has the same 

 attractive force for water as any other diosniotic combination, as for 

 example oxalic acid, which is sufficiently diluted to just induce 

 plasmolysis. Such concentrations of equal tension are said to be 

 "isotonic." Chemically related substances have the same coeffi- 

 cient. If the isotonic coefficient of KNO3 is 3, then it is also 3 for 

 ISTaCl, KCl, in fact for all alkaline salts with one atom of the metal 

 in a rnolecule. For organic compounds such as malic acid, citric 

 acid, acetic acid, the coefficient is 2, as has been determined by 

 actual experiment. For alkaline salts with two univalent acid radi- 

 cles, as for example MgCl^, CaClj, it is 4, etc. De Yries further 

 determined chemically the various combinations in the cell-sap and 

 then found the turgor force exerted by each (sum-total). 



The relation between turgor and growth will be referred to in 

 the chapter on " Physiology of Growth." 



Before entering upon the discussion of the cell-contents it should 

 be noted that the contracting primordial utricle carries with it all 

 the solid constituents of the cell-contents ; also that the priraor- 



' Analyse der Turgorkraft, Pringsbeiui's Jahiblicher, XIV (1884). 



