1968. Wall-tree nails are of several sorts; but the principal are, the small cast-iron nail, in most common use with lists; the flat-headed wrought-iron nail, used either with lists, loops of cord, or mat; and the eyed cast-iron nail (fig. 543.), used with small pieces of spray, dried willow-twigs, or mat ties, as in trellis-training. The chief advantage of this last is its not being so liable to lodge the larvï¾µ of insects as the nails which are used with lists; and that, being once driven, it never requires removal, or occasions the injury of the wall, as the branches may be loosened, or altered, by merely taking out the slips of spray, or cutting the mat-ties. (Caled. Mem., vol. iii,) Some gardeners, instead of using nails, drive an iron stud (fig. 544.) into all the horizontal joints of the brickwork, at the distance of ten feet from one another, with the hole in the stud standing out half an inch from the face of the wall. Through these holes copper wires are tightly stretched from one end of the wall to the other, and to this wire the branches are tied with shreds of matting.