An offer lapses by not being accepted in the mode prescribed, or if no made is prescribed, in some usual and reasonable manner. But, according to section 7, if the offeree does not accept the offer according to the mode prescribed, the offer does not lapse automatically. It is for the offeror to insist that his proposal shall be accepted only in the prescribed offeror to insist that his proposal shall be accepted only in the prescribed manner, and if he fails to do so he is deemed to have accepted the acceptance.