Abnormal morphological features in graft unions of apple trees from 1 to 2 year old have been reported to be associated with different degrees of dwarfism imposed by different rootstock for example, studies on graft unions of dwarfing apple rootstocks, M9, M27 and Ottowa 3, showed that the outter bark of these rootstocks was significiantly thicker than that of the semi-dwarfing MM– 106. Also vascular tissues that developed between the rootstock and scion were arranged in a swirling patent, and became necrotic during subsequent growth of the plant