132 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



molysis. To test whether changes of permeability had 

 taken place in various roots exposed to a succession of 

 temperatures, Eckerson plotted the molecular concentra- 

 tions of sucrose, glucose, and potassium nitrate solutions 

 necessary to produce slight plasmolysis against the several 

 temperatures at which experiments were conducted. The 

 results obtained with Raphanus sativus are shown in 

 Fig. 14. Similar experiments were also performed with 

 other plants, and the temperature at which permeability 

 ceased to increase or began to decrease was noted in each 

 ; 0-42 



10 



40 



50 



20 30 



Temperature. 



FIG. 14. Eaphanus sativus : CURVES SHOWING THE EFFECT OF TEM- 

 PERATURE ON THE PERMEABILITY OF ROOTS TO POTASSIUM NITRATE 

 AND GLUCOSE; ORDINATES INDICATE THE PERCENTAGE WT.-MOL. 

 SOLUTIONS PRODUCING SLIGHT PLASMOLYSIS, AND THE ABSCISSA 

 REPRESENT TEMPERATURES. THE HORIZONTAL GRAPHS REPRE- 

 SENT GLUCOSE. 



case. When these are tabulated and compared with the 

 limits of positive and negative thermotropism of the same 

 roots a very striking similarity is revealed. The following 

 table, quoted from Eckerson's paper, illustrates this. The 

 temperatures recorded are those inside the vessel con- 

 taining the roots. 



In the table + denotes positive curvatures and increas- 

 ing permeability; denotes no curvature and no change 

 in permeability; -- denotes negative curvatures and de- 

 creasing permeability. (K) and ( w ) refer to results obtained 

 by Klercker (1891) and Wortmann (1885) respectively. 



