Effects of Seasonal Changes in Shoot Growth on the Amount of Unsuberized Root on Apple and Plum Trees

Measurement of the white root, visible through glass panels, from young apple and plum trees showed that production of new white root was reduced during periods of intense shoot growth. On the apple trees maximum quantities of white root occurred in May, at about the time of full bloom, and again in August or September after shoot growth had ceased. In contrast, on some of the plum trees with only a few weak shoots, maximum white root was recorded in June and only small amounts of new white root were present during the remainder of the year. The effect of branch pruning was to stimulate more intense shoot growth: the more intense the shoot growth the greater and more prolonged was the reduction in new white root production in mid-summer. The interpretation of these results in terms of the physiological relationship between root and shoot is discussed.