Terumos 1:10-2:1

Terumos 1:10

One may not take terumah from completed produce (stored in a smoothed pile) for uncompleted produce (not yet stored), nor vice versa, nor may one take terumah from uncompleted produce for uncompleted produce. In all of these cases, if one did take terumah, the terumah is valid.

Terumos 2:1

One may not take terumah from ritually pure produce for impure produce but if he did, the terumah is valid. It is accepted halacha that if part of a cake of pressed figs is impure, one may take terumah from the pure part for the impure part (since it is one item). The same is true of a bundle of vegetables or a heap of grain. However, if there were two cakes of pressed figs, one impure and one pure - or two bundles of vegetables or two heaps of grain – then one may not take terumah from one for the other. Rabbi Eliezer says that one may take terumah from the pure one for the impure one.