No. .32-2] 



PHYSIOLOGICAL HESPOXSE 



menting earlier investigations, suggests an answer. 

 Turgor variations have long been studied, but a reason 

 for them has been sought in vain. AVe now know that 

 various agents change the permeability of the protoplast 

 to solutes, and that this sensitiveness is not limited to*the 

 specialized cells of a gland or a motor organ, but char- 

 acterizes even the mesophyll. That this behavior occurs 

 where there is no obvious relation to the functions of the 

 organ, suggests at once that it inheres in the protoplast 

 as a fundamental quality, in virtue of its chemical consti- 

 tution or its molecular structure. It is perfectly easy to 

 understand that this structure may be modified by the 

 radiant energy already known to alter the permeability 

 of the protoplast; and many other stimuli are of a kind 

 to influence the unstable chemical compounds that com- 

 pose protoplasm. If that estimate be verified by further 

 researches, we shall be justified in considering nwiability 

 in permeability as a basic property of protoplasts. 



It will be evident enough that a change in permeability 

 will permit the escape of some of the cell sap, with con- 

 sequent shrinkage of the protoplast, stretched as it is by 



urally result. Whether the escape of the solutes would 

 account for the negative electric variation, I do not pre- 

 tend to say, for the present theories as to electromotive 

 force do not afford any light on the situation. Therefore, 

 until the relation of electric stresses to other phenomena 

 is better known, we must leave this question in abeyance. 

 The primary and secondary phases of a response may 



anisms, or indirectly, by altering the rate of growth, as 

 in growth mechanisms. That the turgor changes re- 

 ported in the root undergoing gvotropic curvature appar- 

 ently do not harmonize with this theory is probably due 



