Plants follow different pathways in response to environment or phases of life to form different kinds of structures. This ability is called :

The correct option is Plasticity.

Step-by-Step Explanation:

1. Understanding the definition: In plants, the growth and development are highly responsive to environmental cues and internal signals. The phenomenon where plants follow different pathways in response to their environment or phases of life to form different kinds of structures is biologically termed as plasticity.

2. Example of Plasticity (Heterophylly): A classic example of plasticity is heterophylly, where the shapes of leaves are different in different phases of life or in different environmental conditions. For instance:
- Phase of life: In cotton, coriander, and larkspur, the leaves of the juvenile plant are different in shape from those in mature plants.
- Environmental response: In buttercup (Ranunculus), the leaves formed in air have a different shape compared to those formed in water.

3. Analyzing other options:
- Elasticity: Refers to the physical property of a material to return to its original shape after deformation, which is not the correct biological term for this growth response.
- Flexibility: Indicates the ease of bending, which does not represent developmental pathway alterations.
- Maturity: Refers to the state of being fully developed or adult, which is a phase of life rather than the ability to change structural pathways.

Hence, the ability of plants to alter their development in response to environment or life phases is called plasticity.