[If] a rosh tor of greens entered into a field of a different [type of] greens, this is permitted since it appears like the end of his field. If his field was planted with greens, and he wants to plant inside it a row of a different [type of] greens — R’ Yishmael says: [Not] until the furrow reaches from one end of the field to the other. R’ Akiva says: A length of six handbreadths and a width equal to its fullness. R’ Yehudah says: A width the full width of a foot.