What is the orientation of growth in response to an external stimulus called?

The orientation of growth in response to an external stimulus is called tropism, which refers to the directional growth movement that occurs in response to a specific environmental factor. This phenomenon can be observed in various plants reacting to light, gravity, water, and other stimuli.

Tropism is broadly categorized into different types based on the stimulus involved, such as phototropism, which is specifically the growth response to light, and geotropism, which pertains to growth in response to gravity. Phototropism and geotropism are examples of functional tropisms, but the term "tropism" itself encompasses all types of directional growth responses that plants exhibit to various stimuli.

Understanding tropism is essential in the field of arboriculture as it highlights how trees and other plants adapt their growth patterns to optimize their chances of survival and growth in their environments.