262 BOTANICAL GAZETTE [September 



together with the temperatures at which there is increasing or 

 decreasing permeability, for each species. In the table, + indicates 

 positive curvatures and increasing permeability; o indicates no 

 curvatures and no change in permeability; — indicates negative 

 curvatures and decreasing permeability. 



The data show that the permeability increase or decrease paral- 

 lels almost exactly the positive or negative curvatures. In every 

 case, at those temperatures which cause positive curvatures there 

 is increasing permeability; where there are no curvatures, there is 

 no change in the permeability; and at temperatures causing nega- 

 tive curvatures there is decreasing permeability. The slight differ- 

 ences in temperature at the turning point are well within the range 

 of experimental error. 



Conclusions 



Wortmann's inability to obtain positive thermotropic curva- 

 tures in the primary roots of Phaseolus multifloriis is explained by 

 the fact that there is no increase in permeability. In the secondary 

 roots, however, where he found positive curvatures, there is an 

 increasing permeability. Klercker obtained no negative thermo- 

 tropic curvatures in Sinapis alba; there is no decreasing permea- 

 bility. Also, Klercker obtained only negative curvatures in 

 Helianthus annuus; there is no increasing permeability, therefore 

 no positive curvatures. 



The permeability of the cells of the root to potassium nitrate 

 and to glucose increases or decreases with increase of temperature 

 according to the species, and for a given species according to the 

 temperature. 



temperature 



more perme 



at one of the temperatures than at the other. Those cells which 



more perme 



able 



to dissolved substances are consequently less turgid. This results 

 in a shrinking of the tissues on that side of the root and a consequent 

 mechanical curvature. Always the more permeable side of the root 

 becomes concave. 



