[If] someone wants to make his field into squares of every species, he can make twenty-four squares in a beis se’ah — each square is a beis rova — and he can plant inside it any species he wants. [If] there were one or two squares, he can plant them with mustard. [If there were] three, he cannot plant [them] with mustard, because it looks like a field of mustard. This is the opinion of R’ Meir. But the Sages say: Nine squares are permitted, ten are forbidden. R’ Eliezer ben Yaakov says: Even if his entire field is a beis kor, he cannot make in it more than one square.