CHAPTER XIV 



Fl 



owering 



Several different paths have led to the discovery that auxins can 

 alter flowering behavior in plants. The influence of auxin on flowering 

 suggests the ultimate possibility of using growth regulators to control 

 or alter flowering in agricultural crops. 



The first demonstration that auxins can affect flowering was 

 by Hitchcock and Zimmerman (1935) who found that flowering of 

 tobacco could be slightly hastened by auxins. The first and only spe- 

 cies which has been found actually to be induced to flower by auxins 

 is the pineapple (Clark and Kerns, 1942), although auxins have been 

 found to alter slightly the threshold daylength required for the 

 photoperiodic induction of some long-day species (Liverman and 

 Lang, 1953). 



There have evolved three different types of auxin applications to 

 influence flowering. In the case of the pineapple, auxins are sprayed 

 on the foliage of vegetative plants, and by this treatment flowering 

 is actually induced. A second method, the foliar application of auxin 

 sprays at the time of normal flower initiation or shortly thereafter, 

 can cpiantitatively increase or decrease the flowering behavior. In this. 

 way the litchi tree can be made to flower more profusely (Shiguera, 

 1948), and the bolting of the sugar beet may be delayed (Price et al, 

 1950). A third method of applying auxins is by soaking seeds in an 

 auxin solution, a technique originally described by Cholodny (1936). 



THE PHYSIOLOGICAL BASIS OF FLOWERING EFFECTS 



There is some evidence that floral initiation is controlled by a 

 hormone. Perhaps the most salient evidence for the existence of a 

 flowering hormone is the fact that photoperiodic stimuli are perceived 

 by the leaves and are thence translocated to buds where the response 

 takes place (Cajlachjan, 1936; Moskov, 1936). The suggestion that a 

 hormone was responsible for photoperiodic induction was made by 

 Cajlachjan (1936). He rather guardedly suggested that the flowering 

 hormone might be auxin, but that has not proved to be the case. 

 Several characteristics of the flower-inducing stimulus have been elu- 

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