SHOOT TIP ABORTION IN ULMUS AMERICANA

摘要: MILLINGTON, W. F. (Marquette U., Milwaukee, Wis.) Shoot tip abortion in Ulmus americana. Amer. Jour. Bot. 50(4): 371-378. Illus. 1963.-Phenological observations of American elm have shown that the phenomencn cf shcot which distal several plastochrons each shoot turn yellow and abort, inducing syrnpcdial growth, occurs over a peried weeks starting at time fruits are shed from older trees. Time varies among plants different age, individuals same shoots on individual. In latter case, is inversely correlated with vigor shoot, most vigorous branch being last to abort. Abortion first evident yellowing entire tip. Cytohistological studies show necrosis commences sixth eighth node back apex, where it apparent autolysis internal cells stipules. Necrosis progresses acropetally stipules young leaves ultimately involves leaf primordia apex. Mitosis ceases apex its meristematic appearance lost. These changes follow basipetal sequence axillary buds down bud below abscission site. This remains active will resume growth following season. The site externally as green-yellow boundary basal part internode. No protective layer present abscissicn, but develops after abscises. There no indication blocking vascular tissues before limitation water supply probably not causal factor. Photoperiod accelerated short days delayed prevented long days. Greenhouse experiments also seedlings, supplied organic fertilizer, or grown roots unconfined. Plants nutrient solution deficient nitrogen aborted ahead controls calcium. Although coincident fruit drop, there relationship. literature relating discussed relation above observations. RECENT investigations effect photoperiod vegetative woody perennials (Nitsch, 1957a,b; Downs, 1958; Wareing Black, 1958) directed attention abortion, morphogenetic phenomenon until recently has had only limited study. many genera (Ailanthus, Betula, Catalpa, Celtis, Cercidiphyllum, Staphylea, Syringa, Tilia, Ulmus) an inherent characteristic induces subsequent development subjacent buds, resulting sympodial pattern typical these genera. Under seasonal stimuli, portion usually including nodes internodes, becomes necrotic may abscise. While described botanical (Kerner, 1895; Goebel, 1905; Buisgen Muinch, 1929), resultant occurrence "pseudoterminal bud" commonly utilized distinguishing taxonomic keys plants, little been written mor1 Received for publication September 17, 1962. Supported by grant National Science Foundation (G16735). Gratitude expressed Dr. J. Talacko, Department Mathematics, Marquette University, assistance statistical analyses, Mr. B. Sparkowski Milwaukee County Park Commission their cooperation some experimental phases this phogenetic aspects (Titman Wetmore, 1955; Garrison 1961). tips elm, americana L., natural takes place spring early summer rapidly decline expanding shoot. Shortly turns abscises base internode (Fig. 1). purpose paper note correlations between environment, age process morphologically clues cause. ABORTION IN RELATION TO PHENOLOGY, AGE, AND VIGOR-In attempt obtain factors induce phenological elms various ages made past few years Madison Wisconsin. timing number events Table 1. Note flower expand advance spring. Fruits begin abscise just parallel internodes fully expanded. trees, mid-May, variable rates depending