The cracks which extend from bark towards the sap wood in the cross section of a tree, are called

ANS:B - star shakes

Cup shakes are formed due to non-uniform growth of a tree or excessive bending by cyclones or winds. In this case, the shakes develop between annual rings and separate them partly.

Heart shakes, the other type of shakes which develop in maturity approaching trees whose inner part is under shrinkage. The shake spread from pith to sapwood following the directions of medullary rays.

Ring shakes are similar to cup shakes, but they completely separate the annual rings.

Star shakes are formed due to extreme heat or severe frost action. They develop wider cracks on the outside of timber from bark to the sapwood.

Radial shakes are developed radially from pith to the bark. Star shakes is the right answer crack from outside (bark) to inside (pith) is star shakes.

Heart shake is from inside (pith) to outside (bark).

Cup shake crackes are formed b/w the annular rings and these cracks seperate the annular rings partially.

Ring shakes similar to cup shakes but the seperation b/w the annular rings is 100%.