AbslraelThe relations between longitudinal growth, Young's modulus, luigor. water potential, and tissue tensions have been studied on growing internodes of etiolated pea seedlings in an attempt to apply some physical concept.s to the growth of a wellknown plant material. The modulus has been determined by the resonance frequency method and expressed as En,^,,,,. It increases nearly proportional to the turgor pressure and is at water saturation more than 50 times higher than at plasmolysis. Etisaue 's higher in the epidermis than in the ground parenchyma. Indoleacetic acid causes a decrease in Etj^suo-Other properties have heen studied on intact and split segments of internodes in solutions of graded mannitol additions. -The following tentative picture of the normal course of the growth has been obtained. Anxin induces growth both in the periphery (epidermis) and in the central core (parenchyma) nnder a decrease in Etiss,,^. This is followed hy tin increase of Etj^s^R which is independent of auxin hut depending upon the turgor pressure. It is assumed to involve internal structural changes of the cell walls of the type of creep. The rapid f,'row(h takes place in a dynamic system with a low water jrotential despite favourable water eonditions. Epideimis and parenchyma grow equally rapid without tissue lensions. -Such can be produced artificially by splitting of .segments and water uptake. The parenchyma thereby loses its sensitivity to auxin. This is the background of the split stem test for auxin. -Etigg,,^ increases when growth is slowing down, probably owing to both synthesis of wall substance and structural changes wilhin the wall. The cells attain a more static condition with E,js^,,,> higher in epidermis than in parenchyma. This leads to the normal tissue tensions. -The result ngrees with growth according to the multi-net-principle. The cause of the low water potential and low tnrgor is discussed with reference to th& dynamic nature of both growth and water transport and a probably low matric potential of tbe streaming water. 'Ihc decrease in En^sue following auxin addition is small but is the net difference between an auxin-induced decrease and an increase through the assumed creep.