The relationship between the form and structure of plants and their gravitational environment is one of the most important teaching subjects of biological education. However, the teaching materials for the gravity effect have so long been concerned only with gravitropism, i.e. the short-time response of adjusting the orientation of seedling roots and coleoptiles axes against the direction of gravity. In this paper, we propose new teaching material that demonstrates the effect of gravity upon the shape, strength and habit of aerial plant axes and the relationship between them. By analysing the static compressive and bending force balances at any cross section of plant axes, we can understand that plants grow by adjusting their shape and hardness of material in order to support their bodies against gravity, according to their growth strategies. This teaching exercise may be useful in enabling undergraduate students to recognise the form and structure of plants' bodies in terms of biomechanical concepts and in leading them to a deep understanding of plant growth and development. (Contains 10 figures.)