To solve this problem, we need to understand the concept of dedifferentiation and how it applies to the formation of interfascicular cambium.$\newline \bullet$Dedifferentiation is the process by which mature, specialized cells revert to a less specialized state, allowing them to regain the ability to divide and form new tissues.$\newline \bullet$In plants, interfascicular cambium is formed from fully developed parenchyma cells located between vascular bundles.$\newline \bullet$These parenchyma cells dedifferentiate to become meristematic, meaning they regain the ability to divide and contribute to the formation of secondary vascular tissues.$\newline$Therefore, the formation of interfascicular cambium from fully developed parenchyma cells is an example of dedifferentiation.$\newline$This corresponds to Option 1: Dedifferentiation.