Maasrot, Chapter Four, Mishnah Five
1) One who husks barley may husk one at a time and eat [without tithing], but if he husked and put them into his hand, he is liable [to tithe].
2) One who rubs [ears of] wheat may blow out [the chaff of the wheat] from hand to hand and eat, but if he blows and puts the grain in his lap he is liable.
3) Coriander which was sown for the sake of the seed, the plant is exempt [from tithes].
a) If he sowed it for the sake of the plant then both the seed and the plant must be tithed.
4) Rabbi Eliezer said: as for dill, tithe must be given from the seed and the plant, and the pods.
5) But the sages say: only in the case of cress and eruca are both the seeds and plant tithed.
Section one: Husking barley and eating the ears one at a time is considered chance eating and therefore one can do so without tithing. However, as soon as he husks the barley and puts several in his hand at the same time, their processing is considered to be completed and he cant eat any of them without first tithing.
Section two: Rubbing ears of wheat is a means to remove the chaff from each ear of wheat. If one does so one ear of wheat at a time, he can eat the individual grains without tithing. However, as soon as he starts to accumulate the wheat in his lap, he is liable for tithes.
Section three: The mishnah now begins to discuss various types of plants whose seeds and plant parts are eaten. The part that needs to be tithed is the part that one intends on eating. If coriander (cilantro) was sown in order to eat the seeds then he needs to tithe only the seeds. He can eat the plant parts without tithing because when he sowed the plant, his intention was to throw these parts away. However, if he sows it in order to use the plant parts, then both these parts and the seeds must be tithed before they can be eaten. The assumption seems to be that in all cases one will make use of the coriander seeds because they are the more valuable part. When someone plants coriander in order to use the plant parts, he is really going to use the seeds as well.
Section four: According to Rabbi Eliezer, one needs to tithe all of the parts of a dill plant, because his intention will be to eat them all.
Section five: The sages disagree with Rabbi Eliezer and with the rule at the end of section three. According to the sages one must tithe the seed and the plant parts of only two species of plant: cress and eruca. When it comes to other plants, either the seed or the plant part must be tithed, but not both.