Some blades, such as the first two, are made with a rounded point to cut the bark without the knife entering the wood underneath. The middle two knives are made with the edge of the knife carrying to a point and are used for ordinary purposes. The last knife has a piece of ivory inserted for opening the bark.
Nicholson, George The Illustrated Dictionary of Gardening, Div. VI (London, England: L. Upcott Gill, 1884)