Observations on the Nature and Development of Structural Defects in the Unions Between Pear and Quince

Abstract

The immediate cause of the mechanically weak unions that occur in some incompatible trees is by now well known. They are due to the abnormal arrangement of the xylem tissue, particularly the fibres, which, instead of interlocking across the union, either curve in a horizontal direction or are separated by a layer of parenchymatous tissue. This has been well described by Proebsting (1928), Bradford and Sitton (1929), Eames and Cox (1945), Herrero (1951) and others. All are agreed that the discontinuity of the vascular tissues is due to some interruption, temporary or permanent, of normal cambial activity at the point of union, but there is as yet little information regarding the basic causes of this interruption. Most anatomical investigations of the union have been concerned primarily with the structure of the woody cylinder, although, as long ago as 1929, Bradford and Sitton wrote, “ the break-down in the bark seems more consistent, more complete and perhaps more important than that in the wood ”. The fi...