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The development of epinastic curvatures in the leaves of various herbaceous species in the presence of low concentrations of ethylene was reported by several workers (3,4,11) before the importance of endogenous growth regulators had been established. Much later an imbalance in the distribution of indoleacetic acid was found to be the basis for epinastic responses in leaves (6) and branches (5) in the absence of an effective gravity vector. It is therefore a reasonable hypothesis that the effect of ethylene on the form and orientation of leaves on erect plants is mediated through interference with the lateral transport of auxin by gravity. Van der Laan (8) found an excess of auxin in the upper half of the horizontal epicotyl of Vicia faba exposed to 5 to 50 ,ul/liter ethylene. Burg and Burg (1) reported an inhibitory effect of ethylene on the downward movement of IAA in horizontal sections of pea stems in the concentration range of 10 to 100 ,ul/liter. Similar lateral transport by gravity in coleoptiles of corn and oats was found to be unaffected by ethylene.The auxin pattern for leaf and branch epinasty had been established by experiments with intact plants rotated on a horizontal clinostat. The reliability of this device for eliminating the transport effect of gravity was confirmed by the results of the clinostat control experiments for the wheat seedling experiment (7) and the leafy plant experiment (4) in Biosatellite II. The hypothesis of ethylene inhibition of the unknown mechanism for downward transport of auxin in leaves can now be tested critically by applying the methods developed for studies in which gravity was not transplanting auxin in rotated leaves. An excess of auxin can be expected in the convex side of an epinastic leaf curvature (6) on an erect plant. METHODS AND MATERIALSPotted plants of tomato (Lycopersicon esculentum Mill.) and pepper (Capsicum annuum L.) at the first flower bud stage were exposed for 23 to 24 hr in darkness to measured concentrations of ethylene. The treatments were carried out inside a sealed chamber with temperature control at 24 i 0.5 C and a capacity of six to eight plants.Pure ethylene was obtained from a pressure tank and supplied to the exposure chamber in measured amounts. The exact concentration in the air around the leaves was determined for each experiment from duplicate samples drawn from the chamber at the end of 45 min. The ethylene content was measured by gas chromatography, using a Perkin-Elmer apparatus with a sensitivity of about 1 ,ul/liter ethylene.The degrees of leaf curvature due to change in orientation of the tip after exposure to ethylene were measured from shadowgraphs. Spotlight shadows of leaf tip markers were traced manually on the same wall-positioned sheet at the start and close of each test period. The angle of epinastic curvature was then meas-

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Summiiiiiary. Seedlings of wheat (Triticum vestivumin L.) were grown in special holders that permitted the coleoptile and early roots to develop in m3ist air. The orientation of the organs of seedlings erect to gravity was compared with that of organs produced on a horizontal clinostat. Orientation was described by the angular position of each organ tip with reference to the axis of the embryo. Comparative tests were also made with barley, rye, and oat seedlings.The coleoptile of all species developed curvatures in 3 dimensions when geotropic responses were eliminated. The primary root was not precise in its positive geotropism.Seedlings grew on clinostats with much greater variations in the lateral orientation of the central root and with a tendency for it to curve awav from the endosperm to a greater degree than in erect seedlings.The symmetry of root system in wheat was found to depend on a specific mechanism. Under the influence of gravity the earliest lateral roots were oriented in a plane at characteristic angles of about 57.5°with the ideal primary root. The corresponding angles for lateral roots growing on clinostats were greater by abotut 47.50 as a result of epinasty not previously reported in roots. This force also appzared to be active in the seminal roots of barley and rye but not of oats.The curvatures in coleoptiles grown without the directional effects of gravity correspond to the results of growth imbalance in Coleus stems in the absence of lateral transport of their auxin by gravity. Root

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