254 Auxins in Agriculture 



cidated experimentally. For example, the stimulus moves principally 

 in the phloem (Cajlachjan, 1938), either up or down a stem (Moskov, 

 1939), its rate of movement can be retarded by low temperatures 

 (Borthwick and Parker, 1941), it can move only in living tissues as in- 

 dicated by the fact that it can cross graft unions only when living 

 connection has been made (Wi throw and Withrow, 1943), and finally, 

 the stimulus of long-day, short-day and indeterminate species has been 

 found to be identical (Lang, 1952). 



In analyzing the physiological characteristics of auxins and the 

 hypothetical flowering hormone, it seems clear that the two are not 

 identical. Several distinctions between them can be drawn: auxins 

 are principally polar in movement whereas the flowering stimulus is 

 not; auxins are diffusible, the flowering stimulus apparently is not: 

 and lastly, compounds which are not auxins can force flowering in 

 pineapple in a manner very similar to auxins (Rodriguez, 1932; 

 Lewcock, 1937). This latter point suggests that even in pineapple the 

 flowering response may not be specific for auxins. 



There have been several suggestions as to the means by which 

 auxins may modify floral initiation. Galston (1947) has suggested that 

 the flowering hormone and the growth hormone may be antagonistic 

 to one another and consequently the application of auxins inhibits 

 flowering. Bonner (1951) has suggested that auxins modify photo- 

 periodic responses of plants by interfering with the night reaction in 

 the leaf. While these suggestions may be valid for inhibitions of floral 

 induction they cannot apparently account for promotions of flowering 

 by auxins. Some evidence mentioned in chapter IV indicates that the 

 effects of auxins on flowering involve an interaction with other plant 

 materials. For example, addition of auxins alone may inhibit flower- 

 ing, but the addition of auxins in the presence of other added mate- 

 rials such as sugars or organic acids may promote flowering (Leopold 

 and Guernsey, 1953). There is a rather striking parallel between these 

 effects and the interaction of auxins and other materials in the control 

 of differentiation of buds (cf. figures 48 and 49, pp. 104, 108). 



CONTROL OF FLOWERING IN PINEAPPLE 



Rodriguez (1932), having observed that brush fires adjacent to 

 pineapple fields stimulated flowering, was led to the discovery that 

 smoke, and specifically unsaturated gases such as ethylene in smoke 

 could bring about flower initiation. In the following year similar 

 experiments in Hawaii revealed that acetylene gas, too, would initiate 

 flowers. This latter material found its first field use for that purpose 



