Simunary. Pea epicotyls (PisuniI satikl'u,,, cv. Alaska) were enclosed in chamibers in which their elongation was restricted by means of a foam neoprene stopper or by a medium of glass beads. These treatmentii increase(l evolution of ethylene and restllted in reduced length and increased dianmeter of both the internodes and the cells of the internodes. These responses increase(d with increasinig degrees of restriction. A time-sequenice study of the emergence of epicotyls through 90 mm of glass beads showed that all accelerated evolution of ethylene precede(d a reduction in elongation. As the epicotyls elongated through the glass bead mediumii and less resistance was encounitered, evolution of ethylenie decline(l and rapid elonigatioi was resumed.

The growth rate of rice coleoptiles is increased by low concentrations of ethylene, especially in oxygen concentrations lower than air; carbon dioxide enhanced this response. C2H4 is produced by rice seedlings, and this production is also enhanced by carbon dioxide. Ethane and propane were produced in trace amounts but were inactive in growth stimulation as were also methane, propylene, and butane.

Dormant potato tubers (Solanum tuberosum L.) of two cultivars were treated with various concentrations of ethylene gas for various exposure periods. As has been shown by others, ethylene caused a rapid but transient increase in respiration rate, which appeared to be independent of any effects on dormancy. All concentrations tested caused accelerated sprouting, 2 microliters per liter being the most effective. Ethylene exerts a dual effect on potato tubers: it markedly shortens the duration of rest, but it inhibits elongation of the sprouts during extended treatment. Comparing these results with published work on seeds, bulbs, and corms suggests that ethylene must have a significant but as yet unexplained role in rest and dormancy. However, since the most effective ethylene treatment did not equal the response elicited by treatment with ethylene chlorhydrin, other factors must also contribute to termination of rest.The initiation of sprouting in potato tubers is accompanied by a variety of biochemical changes which are usually reflected in changes in hormonal concentration, respiration rate, and the onset of nucleic acid synthesis and cell division and enlargement (16, 21, 24-26, 30, 31). A number of reports have supported the hypothesis that the rest period in potato tubers is regulated by gibberellins and ABA (24,26,30). However, the significance of other hormones, particularly of ethylene, has not been investigated adequately.That ethylene is an endogenous growth hormone for plants and a potent growth regulator is well established (1,23), but its role in the dormancy of potatoes and other plant organs has remained unclear. The older works on potato present conflicting evidence (4, 5), and there has been little clarification in recent work. Terminating dormancy in freshly harvested potatoes is an important practical problem, to which much attention has been given, and many chemical treatments have been tried (5,22). Rosa (28) was first to try ethylene; concentrations of 10, 200, and 1000 ,ull were applied for 28 days giving substantial increases in the stand obtained 1 month after planting. On the other hand, Denny (8, 9) tried ethylene, propylene, and acetylene at 1000 and 10,000 ,lll for 4 and 7 days and found them to be ineffective. In studies by Vacha and Harvey (32), ethylene treatments with 1000 ,ul/l at 20 C for 6 days gave 'This investigation was supported in part by North Atlantic Treaty Organization Research Grant 541 to L.R.2 On leave from Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. earlier sprouting and faster growth with some potato cultivars. Rosa (29) reported further tests with ethylene, using treatments of 455 and 2500 ,ul/l for 2, 3, or 4 weeks at 22 C; the 2-and 3-week treatments inhibited sprouting, whereas a 4-week treatment promoted sprouting (no difference between the concentrations was observed). In a better planned experiment with 800 ,1/1, ethylene accelerated emergence, especially in the shorter treatments. Another experiment with 500 1ul/l g...

Abstract. The relationship among gibberellins, C vernalization, and photoperiod in the flowering response of radish, Raphanus sativus L., cv. Miyashige-sofuto, was studied. The optimal condition for flowering was vernalization and a 16-hour photoperiod; GA3

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