Mendel obtained plants that were true-breeding for particular traits by repeatedly self-pollinating plants that exhibited the desired trait over multiple generations.

Here's a breakdown of how this works:

* True-breeding: A true-breeding organism produces offspring with the same trait as itself when self-pollinated. This means the organism is homozygous for the trait (has two identical alleles).

* Self-pollination: The transfer of pollen from the anther of a flower to the stigma of the same flower.

* Multiple generations: By repeatedly self-pollinating plants that showed the desired trait, Mendel ensured that any offspring that did not exhibit the trait were eliminated, leaving only plants homozygous for the desired trait.

This process allowed Mendel to establish his famous "pure lines" of pea plants, which formed the basis of his groundbreaking experiments on inheritance.