Abstract: The sealing of plastic bags filled with a particular product, for example bread, is commonly achieved by folding a length of adhesive tape (1) around the gathered neck (10) of the bag. The adhesive tape (1) is folded such that the ends of the tape stick to each other to form a closed loop. A bag tying machine for sealing bags in this way includes a roll of adhesive tape (1) having spaced portions (3) which are non-adhesive, wherein the tape is wholly coated with adhesive and the non-adhesive portions are portions which have been treated to neutralise the adhesive; a detector (14) for detecting the boundary between the adhesive and non-adhesive portions of the adhesive tape (1); and, cutting means (13) for cutting the adhesive tape (1) into individual ties wherein the cutting means (13) cut the tape (1) at positions according to boundary position data received from the detector (14).