Seasonal Cycle of Phloem Development in Woody Vines

Seasonal collections of stems of various ages were made of Celastrus scandens L., Parthenocissus inserta (Kerner) Fritsch, and Vitis riparia Michx. In C. scandens, cambial activity, phloem differentiation, and xylem differentiation begin in early May. Phloem and xylem differentiation is completed by mid-August. Cessation of function of phloem begins in mid-October. By late December all mature sieve elements are dead. In P. inserta, cambial activity and phloem differentiation begin in early April New xylem differentiation begins in late May. Differentiation of phloem and xylem is completed by early August. Cessation of function of phloem begins in early October, and by mid-December all sieve elements are dead. In V. riparia, sieve elements usually function for more than 1 year. In early April, reactivation of overwintering sieve elements begins. Cambial activity begins in late June, followed by phloem differentiation, which begins in early July. Xylem differentiation begins about a week later. Cessation of function of the reactivated phloem begins in late July. New differentiation of phloem and xylem is completed by mid-August. Dormancy callose occludes the pores of the present season's sieve elements during October.