114 ISOTONIC COEFFICIENT. [CH. V 



condition when the plasmolysing fluid is replaced by 

 water. A few simple observations on roots of V. faba 

 serve for this purpose. A bean root about an inch in 

 length is placed in 5 "/o NaCl solution, where it almost 

 immediately becomes soft and flaccid. When replaced in 

 water it quickly becomes turgid again ^ 



The observations here suggested are meant as illustra- 

 tions of the very simplest aspect of turgor, chiefly to 

 show that turgor is an osmotic phenomenon, since the 

 condition of the cell is clearly regulated by the relation 

 between the cell sap and the environing fluid. 



(148) Osmotic strength of cell sap in terms of KNO3. 



The method of de Vries^ depends on the fact explained 

 in experiment 163 (Section C) that when a turgescent 

 shoot is bisected longitudinally each half curves outwards, 

 i.e. with the epidermis on the concave side. If the 

 curved portions are put in water the curvature increases 

 greatly : if they are placed in strong NaCl solution (5 °/o) 

 they uncurl, i.e. become straight again, or they may even 

 become convex on the epidermic side. Therefore an 



IntSroediate'stfragtirof'salysoluKoh must be discoverable 

 which equals the celTsap in~osm6tic force, and which 

 neither produces increase nor decrease in curvature. 



1 In summer we use the scape of the dandelion. 

 Taraxacum ; in winter the hypocotynoI^TEiSniis. The 



1 We have observed the root of the bean, if placed alternately in salt 

 solution and water several times, becomes translucent, being in fact 

 injected with water. It would seem that the collapse and re-turgescence 

 of the cells act like a pump and fill the intercellular spaces. 



^ Pringsheim's Jahrbucher, xiv. 



