212 DROSERA ROTUNDIFOLIA. [Chap. X. 



moderately rigid and elastic; if bent by a needle, the upper 

 end yields more easily than the basal and thicker part, which 

 alone is capable of becoming inflected. The rigidity of this 

 basal part seems due to the tension of the outer surface bal- 

 ancing a state of active and persistent contraction of the 

 cells of the inner surface. I believe that this is the case, 

 because, when a leaf is dipped into boiling water, the ten- 

 tacles suddenly become reflexed, and this apparently indi- 

 cates that the tension of the outer surface is mechanical, 

 whilst that of the inner surface is vital, and is instantly de- 

 stroyed by the boiling water. We can thus also understand 

 why the tentacles as they grow old and feeble slowly become 

 much reflexed. If a leaf with its tentacles closely inflected 

 is dipped into boiling water, these rise up a little, but by no 

 means fully re-expand. This may be owing to the heat 

 quickly destroying the tension and elasticity of the cells of 

 the convex surface; but I can hardly believe that their ten- 

 sion, at any one time, would suflace to carry back the ten- 

 tacles to their original position, often through an angle of 

 above 180. It is more probable that fluid, which we know 

 travels along the tentacles during the act of inflection, is 

 slowly re-attracted into the cells of the convex surface, their 

 tension being thus gradually and continually increased. 



A recapitulation of the chief facts and discussions in this 

 chapter will be given at the close of the next chapter. 



