EFFECTS OF GIBBERELLIN AND AMO-1618 ON 



GROWTH AND FLOWERING OF Chrysanthemum 



morifoUiim ON SHORT PHOTOPERIODS 



HENRY M. CATHEY 



Agricultural Research Service, United States Department of Agri- 

 culture, Beltsville, Marjland 



Chemicals that modify the growth of plants have interested physiolo- 

 gists for many years. Among these growth regulators is gibberellin 

 (Kurosawa, 1932), which is effective in accelerating elongation and 

 flowering of many kinds of plants (Marth et al, 1956). Several nico- 

 tinium and quaternary ammonium compounds have been reported 

 (Mitchell et al, 1949; Wirwillie and Mitchell, 1950) to inhibit elonga- 

 tion of a limited number of kinds of plants. The most active of these 

 compounds, (4-hydroxy-5-isopropyl-2-methylphenyl) trimethylam- 

 monium chloride, 1-piperidine carboxylate, has been designated Amo- 

 1618.^ Application of Amo-1618 greatly inhibited elongation and de- 

 layed flowering as compared with the development of untreated plants. 

 Among the responsive plants were chrysanthemums, short-photoperiod 

 plants (Marth et al, 1953). Later, Marth and Mitchefl concluded 

 from unpublished data that gibberellin and Amo-1618 applied in a 

 lanolin paste were mutually antagonistic on the stem elongation of 

 pinto beans. The photoperiod-controlled effects of gibberellin and 

 Amo-1618 on the growth and flowering of Chrysanthemum mori- 

 foUum were studied in the experiments reported here. 



GENERAL MATERIALS AND METHODS 



Rooted chrysanthemum cuttings planted in 3-inch pots containing 

 a mixture of soil and peat were grown in a greenhouse where the mini- 

 mum night temperature was 15.6°C. They were kept on long photo- 



1 Amo-1618 was supplied by the Growth Regulator and Antibiotic Labora- 

 tory, Crops Research Division, Agricultural Research Service, Beltsville, Mary- 

 land. 



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