Orlah, Chapter 3, Mishnah 4. Our Mishnah deals with a cooked dish that was cooked using orlah peels, and with its status when it becomes mixed with other foods.
"Tavshil shebishlo bikelipei orlah":
This refers to a food that was cooked using the peels of orlah fruit as fuel. As we mentioned earlier, the peels of orlah fruit are themselves forbidden to derive benefit from, and therefore a dish cooked with them must be burned and may not be used. The reason is the principle of 'shevach etzim betavshil' - the benefit provided by the fuel is considered to be present in the dish, in the cooked food, and for that reason the food itself becomes forbidden to derive benefit from as well.
"Nisarev ba'acherim - ya'aleh be'echad umasayim":
If that dish became mixed with other foods, and we do not know which of the foods is the one forbidden on account of orlah, it is nullified in a mixture of two hundred and one.
The commentators explain that here even Rabbi Meir agrees that the item is nullified. Rabbi Meir was stringent earlier and ruled that a piece of cloth is not nullified, because a piece of cloth or a thread is considered a significant, important item; here, however, the cooked dish is not considered significant, or alternatively the orlah peel that was used as fuel is not considered an important item. Therefore even Rabbi Meir would agree here that the mixture is nullified.
In summary: In this Mishnah we learned that a dish cooked with orlah peels must be burned, since 'shevach etzim betavshil' and the dish becomes forbidden to derive benefit from; and if it became mixed with other foods, it is nullified in two hundred and one. Even Rabbi Meir agrees to this, because there is no significant item here that would prevent the nullification.