Petiolar Glands in the Plum

Abstract

Examination of over 30,000 leaves belonging to 15 species and interspecific hybrids of the plum shows that two glands typically occur on the petiole, or less frequently on the leaf base. On the basis of vascular connections the glands on the petiole or leaf base are of a different order of structure from those on the leaf serrations. The stipules in the plum are morphologically integral with the leaf base, and separate from the stem by a common abscission layer. A portion of the node bearing the leaf and stipule scars is subsequently shed in some species of Prunus as in other woody genera; but the portion thus shed is not an additional foliar element. On the basis of nodal anatomy and the presence of reduced structures, the ancestral type of leaf in the plum is considered to be a ternate lobed or divided simple leaf, the petiole glands representing the suppressed lateral members. In floral structure and nodal anatomy Prunus and related genera form a logical series with the Potentilleae, and should be considered as a specialized tribe of the Rosaceae.