Tosefta sobre Terumot 1:7

We do not take terumah from produce [that is harvested] before it is one-third ripe (cf. Hallah 1:3). How do you know if it is one-third ripe or if not? If it is planted and something has sprouted, it is known that it one-third ripe. If it is planted and something has not sprouted, it is known that it is not one-third ripe.

[If] he had a pile of winnowed [grain], and he wanted to designate [some of] it as terumah on behalf of [grain in] another place, he does it. He removes the terumah [and] if he [then] wanted to designate [some of the pile] as first tithe on behalf of [grain in] another place, he does it. He removes the first tithe, [and if] he wanted to designate [some of the pile] as second tithe on behalf of [grain in] another place, he does it. He removes the second tithe, [and if] he wanted to to designate [some of the pile] as poor person's tithe on behalf of [grain in] another place, he does it. And if he said, "Behold, [the grain that I pick up shall be terumah, etc.]," he takes terumah and he calculates -- if what he has picked up with his hands is [at least] one sixtieth [of the grain in the other place], his terumah is [valid] terumah, and if not, his terumah [is not] valid terumah. [If when] he took terumah, what he picked up with his hand was [at least] one-sixtieth, his terumah is [valid] terumah, except if he took terumah by measuring (see Ter. 1:7).

One who separates terumah and first tithe and second tithe, and does not know which is which, behold, he may measure the terumah, the first tithe, and the second tithe [in order to determine which pile is which (as a last resort, despite the general prohibition against measuring terumah, Ter. 1:7)].