DENDROLOGY

Detailed explanation-1: -This type of tropism is called gravitropism. Roots of a plant grow downward and exhibit positive gravitropism. Stems, on the other hand, exhibit negative gravitropism since they grow upwards and against the force of gravity (see Figure 1).

Detailed explanation-2: -Gravitropism ensures that roots grow into the soil and that shoots grow toward sunlight. Growth of the shoot apical tip upward is called negative gravitropism, whereas growth of the roots downward is called positive gravitropism.

Detailed explanation-3: -Plant tropism is the general phenomenon of directed growth and deformation in response to stimuli. It includes phototropism, a reaction to light (1); gravitropism, the reaction to gravity (2, 3); and thigmotropism, a response to contact (4), among many others (Fig. 1).