The hypothesis that the rehydration process reflects the changes incurred to the plant material by drying has been proved. Creation of space with larger surface area made by mechanical destruction of internal structures is the evidence of physical changes occurring in plant materials during drying. Different course of water imbibition, way of mass and volume increase, change of the state of equilibrium between crystalline and amorphous regions are the confirmation of physicochemical changes. Leaching of solubles and the loss of plant tissue respiration ability confirm biological changes in dried materials.