Mosaic Variation Plum Leaf
Occasionally a seedling shows a mottled leaf like this. Such a seedling, although otherwise promising, is rejected. In this case vigor of growth in the tree is indicated by the size of the leaf and wood, but a leaf of uniform dark green color is to be preferred. This is interesting, however, as showing a peculiar segregation of color factors, one of the ancestors having been a purple-leaved plum.
This image is from: Luther Burbank: his methods and discoveries and their practical application. Volume 5 Chapter 8