Assertion (A) : In plants differentiation is open.         

Reason (R) : Cells arising out of same meristem have different structures at maturity.

Assertion (A) is true. In plants, differentiation is open, meaning that cells retain the capacity to change their fate and become different cell types under appropriate conditions.

Reason (R) is true. Cells originating from the same meristem can undergo diverse differentiation pathways, resulting in different structures at maturity. This plasticity allows plants to adapt to various environmental cues and developmental needs.

Differentiation in plants is open, because cells/tissues arising out of the same meristem have different structures at maturity.

A and R are true and R is the correct explanation of A.