In the cross-section of timber, which type of shake consists of cracks that originate at the bark and run inward along the medullary rays toward the interior? Identify the shake by its typical star-like pattern on the end surface.

Introduction / Context:
Shakes are natural splits in timber that affect serviceability and grading. Recognizing their patterns helps in selection and in diagnosing seasoning or growth defects. This question distinguishes among common shake types by location and direction of the cracks on the log's cross-section.

Given Data / Assumptions:

• Observation is on an end cross-section.
• Cracks initiate at or near the bark and progress inward.
• Medullary rays guide crack direction, producing multiple arms like a star.

Concept / Approach:
Star shakes characteristically start at the periphery (bark) and extend inward along medullary rays, often producing a star-shaped pattern. By contrast, radial shakes more commonly originate at the pith and run outward. Heart shakes start at the center and move toward the sapwood. Cup (ring) shakes follow the annual rings, creating concentric separations rather than radial lines.

Step-by-Step Solution:

Verification / Alternative check:
Timber grading manuals depict star shakes as outward-origin cracks, often associated with seasoning stresses or weathering entering from the outside, producing the characteristic star-like arrangement.

Why Other Options Are Wrong:

• Radial shakes: typically start at pith and extend outward.
• Heart shakes: originate at the heart (center) and run to sapwood.
• Cup (ring) shakes: run tangentially along annual growth rings forming arcs or closed rings.

Common Pitfalls:
Confusing star and radial shakes due to both having spoke-like lines; the distinguishing clue is the origin point (bark for star, pith for radial).

Final Answer:
Star shakes