[If] one separates part of the terumah or tithes [due from a pile of produce], he may separate from [the pile] the [remaining] terumah for [this pile], but not for another place. R' Meir says: He may even separate terumah and tithes [from this pile] for another place.

One whose produce was in the storeroom, and he gave a seah to a Levi and a seah to a pauper, he may separate up to eight seahs and eat them. [These are] the words of R' Meir. But the Sages say: He separates only according to the amount [of one meal].