“ ROLLER. For agricultural purposes the roller formerly consisted of a solid cylinder of timber or stone attached to a frame and shafts, but to facilitate turning two or more iron cylinders revolving on an axle are now generally used. The simplest form has a smooth surface. The diameter of the drum should be as great as possible—30 in. being a good size—because the larger this is the more easily it is pulled (within certain limits) , while rollers of small diameter are heavier of draught and do their work less efficiently. ”