PHOTOPERIODIC CONTROL OF FLOWERING 283 



Table VL Dependence of Repromotion of Floral Initiation in Plants of Indianapolis 

 Yellow Chrysanthemum on Duration of Darkness between 3-Min Irradiations with 



Red and Far-Red-Radiant Energy 



Relative Stage" of Floral Development 



viously be prevented even though the initial photoreaction is reversed. 

 In chrysanthemum this period is about an hour. 



Repeated Reversibility of Flowering Response 



The flowering response hke other phenomena controlled by the red, 

 far-red reaction is repeatedly reversible. In an experiment involving 

 two varieties of chrysanthemum the lots of plants were given various 

 numbers of alternating 3-min irradiations with red and far red as 

 shown in Table VII. One variety, Honeysweet, was similar to 



Table MI. Repeated Reversal of Flowering Response of Chrysanthemums 

 by Alternating Treatments of Red and Far Red 



Relative Stage" of Floral Development 



Treatment 



R 



R, FR 



R, FR, R 



R, FR, R, FR 



R, FR, R, FR, R, FR, R 



R, FR, R, FR, R, FR, R, FR 



Dark control 



" Values are totals for 6 plants. See text for description of stages of development. 



Indianapolis Yellow in that its flowering was completely inhibited by 

 3 min of red and incompletely promoted by 3 min of far red. Flower- 

 ing of the other, Harvest Golden, was only partly inhibited by 3 min 

 of red, but it was reasonably well repromoted by 3 min of far red 



