Your questions embrace very wide subjects. The cause of canker is generally considered to be a cold wet subsoil. Reasoning from these premises, thorough drainage and planting on slightly-raised mounds of earth to increase the temperature of the soil is the remedy. Some sorts of fruit-trees are much more subject to canker than others, and such varieties as thrive best in any such soil as referred to above, should predominate in forming a collection. Crown and whip grafting are the best methods of grafting Pears and Apples.