Yevamos, Chapter 9, Mishnah 5. This mishnah too is taught according to the view of Rabbi Meir regarding eating Maaser, and it surveys various situations of a woman at different stages of marriage and childbirth: when she is permitted to eat Terumah and Maaser, and when they become forbidden to her.
A daughter of a Yisrael who married a kohen:
"Bas Yisrael she'nis'ah l'kohen - tochal bi'Terumah" - once she married a kohen and the marriage was completed, she eats Terumah by virtue of her husband the kohen.
"Meis v'lah mimenu ben - tochal bi'Terumah" - even after her husband's death, as long as she has a son from that kohen, she continues to eat Terumah.
She married a Levi:
"Nis'ah l'Levi - tochal b'maaser" - from now on she eats Maaser by virtue of her husband the Levi, but she no longer eats Terumah, since she married someone who is not a kohen.
"Meis v'lah mimenu ben - tochal b'maaser" - by virtue of the son she has from the Levi she continues to eat Maaser. Rabbi Meir's view is that only a Levi, or one who is married to a Levi, or one who has a son from a Levi, may eat Maaser. Terumah, however, she does not eat, since she has a son from someone who is not a kohen.
She married a Yisrael:
"Nis'ah l'Yisrael - lo tochal lo bi'Terumah v'lo b'maaser" - once she married a non-kohen and non-Levi, both became forbidden to her.
"Meis v'lah mimenu ben - lo tochal lo bi'Terumah v'lo b'maaser" - even after his death, the son she has from the Yisrael prevents her from eating both Terumah and Maaser.
The death of the sons - working back in reverse:
"Meis benah mi'Yisrael - tochal b'maaser" - once the son from the Yisrael died, she returns to eating Maaser, since the son from the Levi is still alive.
"Meis benah mi'Levi - tochal bi'Terumah" - once the son from the Levi died as well, she returns to eating Terumah, since she is left with no son from anyone who is not a kohen, only the son from the kohen.
"Meis benah mi'kohen - lo tochal lo bi'Terumah v'lo b'maaser" - once the son from the kohen died too, she again eats neither Terumah nor Maaser, since she is left with no sons at all, neither from the kohen nor from the Levi.
In summary: in this mishnah we learned that a woman's right to eat Terumah and Maaser is determined by her husband during his lifetime, and by her sons after his death. Each new marriage changes her status, and each death of a son returns her to the status that comes from the earlier son who remains alive, until she is left with no son either from the kohen or from the Levi, and then both become forbidden to her.