We are reminded of a reed, the quill of a feather, an antler, a long bone of an limb. Tubes are light and provide stiffness, although they do have a tendency to collapse and kink in the middle if they have to support any weight, especially if the tube is long. The weight a tubular column will support, is in fact inversely proportional to the square of its height. The hollow shaft of the femur gets progressively thicker towards the middle to prevent collapse at this weak point of the tube. Tubular structures can be strengthened by longitudinal fibres.
Plant stems are responsive to the loads applied and can increase the amount of fibre if necessary.
Thompson found that young sunflower stalks broke if loaded with 160 gms. If loaded, but not fractured, by say 150 gms for 2 days the load on the stalk increased to 250 gm without causing fracture. Growth may be coordinated with the structural adaptations required by mechanical requirements . This principle is, a fair prophesy of work which has only emerged towards the end of this century which identifies internal bone strain as a stimulus for deposition. If lines of stress are studied by engineers they can be used to predict the design required to relieve them.