To determine the invariable component of a tree: (1) Shadow: Shadows depend on light sources and are absent in darkness. (2) Leaves: Leaves are seasonal and may be absent in young or atypical trees. (3) Fruits: Not all trees produce fruit, and fruit production is seasonal and age-dependent. (4) Roots: Roots are essential for anchoring and nutrient absorption; a tree cannot live without them. Thus, roots are the constant component, matching option (4).