Hooker: Movement in Drosera rotundifolia 399 



3. Alteration of cell-wall elasticity 

 In the opinion of Noll ('95, p. 65) the change in the plasticity 

 of the cell-wall is analogous to the gradual change that takes place 

 in a strung bow, which after having been left strung a long time 

 does not return completely to its original shape when unstrung. 

 This plastic change does not involve any permanent diminution 

 of elasticity, however, for the bow returns to its new shape after 

 bending. The source of energy for this change in plasticity is 

 found in the stored energy of elastic tension. The change from a 

 condition of elastic tension to a plastic alteration of shape is 

 compared by Noll ('95, pp. 79-81) to changes produced in rubber 

 by vulcanization, during which process any elastic deformations 

 that happen to be present are transformed in a greater or less 

 degree to permanent alterations of shape. In bending plant 

 organs he assumes that the protoplasm secretes one or more 

 substances which act on the cell-wall as vulcanizing sulphur acts 

 on crude rubber. 



The correlation between the molecular structure and the 

 physical properties of metals, which has been discovered in recent 

 years by metallographists, ofifers a more satisfactory interpretation 

 of the changes in the physical properties of the cell-wall. The 

 alteration of the strength, ductility and elasticity of metals pro- 

 duced by mechanical treatment and by heat are based on changes 

 in molecular structure, which consist in the rearrangement of the 

 relative amounts of the phases that enter into the composition of 

 the metal. Two phases are usually present, a crystalline phase 

 and an amorphous phase that cements the crystals together. The 

 strength and ductility of a metal are found to be increased and the 

 elasticity diminished by an increase in the amount of the amor- 

 phous phase and a decrease in the amount of the crystalline phase. 

 Conversely the elasticity would be increased and the strength and 

 ductility diminished by an augmentation of the crystalline phase 

 and a decrease in the amorphous phase. It is probable that 

 changes in the elasticity of plant cell-walls are also produced by 

 alterations in the molecular structure. The cell-wall is undoubt- 

 edly a mixture of phases in heterogeneous equilibrium. It seems 

 plausible that changes in elasticity are effected by a readjustment 

 between these phases. Possibly an amorphous and a crystalline 



