Studies in Shoot‐tip Abortion: Syringa Vulgaris

G arrison , R hoda (Wheaton Coll., Norton, Mass.), and R alph H. W etmore . Studies in shoot‐tip abortion: Syringa vulgaris. Amer. Jour. Bot. 48(9): 789–795. Illus. 1961.—The growth of shoots of Syringa vulgaris is described with special reference to the sequence of events in the abortion of the tip. Early in the growing season, as the shoot begins to elongate, the terminal part, 4–7 mm in length and bearing 3 or 4 pairs of young leaves, ceases growth; then after 2 or 3 wk in which there is no change in form, the tip becomes yellow and disintegrates. Diffusible auxin is present in the terminal region as a shoot begins to elongate, but after the abortive phase is initiated, auxin can no longer be detected in that part. Young shoots and tips of shoots when cultured in nutrient media ultimately abort in the normal manner. Shoot tips in the early stages of abortion can be stimulated to resume growth and development if the axillary buds just subjacent to the tip are destroyed; this response is, however, limited to vigorously growing shoots.