90 • Floral Hormones and the Induced State 



pursuit of this kind of work may eventually clarify the relation 

 of auxins and similar substances to flower initiation. 



Another approach is shown in the work of Konishi (1956). His 

 studies of auxin level in several LDP (Sileiie, Rudbeckia, Spinacia) 

 were based entirely on biological assays without previous separation 

 of possible multiple substances, but he also considered enzyme 

 systems that might be involved in the synthesis and destruction of 

 the known auxin, indoleacetic acid. Increased activity of the former 

 and reduced activity of the latter were associated with the "bolting" 

 —rapid stem elongation— characteristic of flowering in many LDP; 

 evidence is lading, however, that these changes actually cause 

 bolting and flowering. 



Some indirect evidence of a role for auxin in flowering has 

 been obtained with radiations believed to affect auxin concentra- 

 tion, including both ultraviolet (UV) and x-rays. As early as 1887, 

 Julius Sachs concluded that UV promoted flowering, since both 

 Tropaeolum (nasturtium) and Lepidium flowered readily in sun- 

 light filtered through water but not through a colorless solution of 

 cjuinine, which absorbs UV. The flowering of Linum usitatissimum 

 (flax) and Statice bonduelli is greatly hastened by exposure to a 

 minute or two of intense UV each day, according to von DenfTer 

 and Schlitt (1951). Supporting von Denfter's (1950) idea that auxin 

 is a major inhibitor of flowering, they concluded that this effect of 

 UV was due to an inactivation of auxin within the plants, and 

 believe it explains the rapid flowering occasionally encountered at 

 high altitudes where more UV readies the vegetation. Many other 

 plants tested, however, did not respond in this way. An example of 

 the promotion of flowering by low x-ray doses, known to reduce 

 ;iuxin synthesis, is reported by Leopold and Thimann (1919); 

 flowering in Wintex barley was increased by over 20 percent after 

 three weekly treatments with 25 roentgens. 



Further indirect evidence comes from the eflects of gravity. 

 Cieotropic stimulation is known to cause a changed pattern of 

 auxin distribution in plants, although the mechanism is unknown 

 (see Audits, 1959; Leopold, 1955); it can also hasten flowering. The 

 Cabezona variety of pineapple (Ananas comosus) can be brought 

 to flower at any time by bending the stem into a horizontal position 

 and keeping it bent for as few as three days; assays confirm the 

 assumption that this treatment results in auxin redistribution (van 



