256 Auxins in Agriculture 



plants did not. In November, when pineapple plants normally initiate 

 flowers, the application ot relatively concentrated auxin sprays (500 to 

 1000 mg./l.) inhibited or entirely prevented flowering. 



The pineapple normally initiates flowers when temperatures are 

 low and photoperiods are short. Each of these environmental factors 

 influences flower initiation, but temperature appears to be the 

 stronger control (van Overbeek and Cruzado, 1948). 



It has been proposed that flowering in pineapple is brought about 

 both naturally and artificially by the accumulation of auxin at the 

 stem apex. Some neat evidence to support this concept is the finding 

 that a pineapple plant placed horizontally will be induced to flower 

 (van Overbeek and Cruzado, 1948). Presumably the reorientation of 

 auxin at the stem apex associated with the geotropic response pro- 

 duces a net increase in the auxin present on the nether side, and the 

 increased auxin level results in floral initiation. The theory is in 

 agreement with the finding that auxin sprays can induce flowering. 

 However, the effectiveness of ethylene and acetylene is unsettling to 

 the theory, especially in view of the fact that no increase in auxin 

 content of the stem tip has been found following ethylene treatment 

 (Leopold, 1949). 



Methods 



Ethylene has been used extensively to force pineapple plants to 

 flower in Hawaii. The method of application involves 4% ethylene 

 adsorbed on a Bentonite suspension in water. The gas is bubbled 

 through the Bentonite suspension, becoming adsorbed on the clay 

 particles, and the mixture is subsequently sprayed on the foliage. 

 Acetylene has been applied in a water and clay suspension as well, but 

 a much simpler method is by the application of dry calcium carbide. 

 Approximately one gram of the calcium carbide powder is dropped 

 into the heart of each pineapple plant where there is commonly a 

 small reservoir of rain-water. The calcium carbide reacts vehemently 

 with the water producing liberal amounts of acetylene, and forcing 

 the plant into floral initiation. 



The use of auxin to force flowering in pineapple can be effectively 

 carried out with any of a large variety of auxins such as naphthalene- 

 acetic acid, indolebutyric acid, and 2,4-dichlorophenoxyacetic acid. 

 Indoleacetic acid is almost entirely ineffective in forcing flowering, pre- 

 sumably because of the presence of large amounts of auxin-destroying 

 enzymes in pineapple tissue as reported by Gordon and Nieva (1949). 

 In Puerto Rico, 2,4-D in concentrations of from 5 to 10 mg./l. has 

 been recommended (van Overbeek, 1946) and in Hawaii 25 to 30 



