Abstract
Plant roots were grown in a modified triaxial apparatus and were subjected to a range of confining hydrostatic stresses. It was found that confining pressures around 3 lbf/in
2 were reasonably well tolerated by the roots, but as the pressure was increased beyond this value root elongation was rapidly attenuated until at pressures beyond 9 lbf/in
2 root growth was almost completely arrested. It was observed that roots thicken under constraint and a hypothesis has been developed to account for the mechanics of root penetration in compact granular media.