(Mishnah): If a person bought two trees in a field, he does not acquire the land as well.

R. Meir: He does acquire the land.

If the trees grew, the seller may not cut the branches (even if they are harming his field). The buyer owns anything that grows from the trunk and the seller owns anything that grows from the roots. If the trees died, the buyer does not own the land (so he may not plant new ones).

If he bought three trees, he also acquired the land. If the trees grew, the seller may cut the branches. The buyer owns anything that grows from the roots. If the trees died, the buyer owns the land (and may plant new ones).

(Gemara) - D'Bei R. Yanai: The part of a tree that sees only shade (as it is under the ground) is considered the roots (and belongs to the field owner); the part that sees the sun is considered the trunk (and belongs to the tree owner).

R. Chama bar Ukva citing R. Yosi: Even if this growth sees the sun when it comes out of the top of the root, since its growth comes from the root, it is considered to be the root and belongs to the field owner. But if it grows from the trunk rather than the roots, it is part of the tree.