[If] one eats a kezayis of matzah [of these species] on Pesach, he has discharged his obligation; [if one eats] a kezayis of chametz [of these species], he is liable to kares. [If] one of these [five species of grain] was mixed with another type [of food], this [person who possesses the mixture] transgresses on Pesach.  [If] one vows [to abstain] from “bread” or from “tevuah,” he is forbidden to [eat bread made from] these [Five Species], [these are] the words of R' Meir. But the Sages say: One who vows [to abstain] from “dagan” is forbidden only to [eat] these [species].  And they are obligated in challah and in tithes.