Question

why do we say that homozygous plants produce pure progeny

Answer 1

Homozygous plants have only one type of trait that is (TT) when they are self polinated then the progeny produced are pure since no other traits are there

Answer 2

According to the biological definition of the homozygous plants,we came to know that ,in these plants there are always a pair of either two dominant traits or two recessive traits.We cannot see any mixture of dominant and recessive traits in these homozygous plants.

That's why say that the homozygous plants produces pure progeny.(Here we are talking about the genetical characteristics purity)