280 CONTROL OF REPRODUCTION 



Table IL Inhibition of Floral Initiation in Indianapolis Yellow Chrysanthemum 



by Red Light 



Period Stage" of Flowering of 6 Individual Plants 



of Irradiation Total for 



with Red, Min 12 3 4 5 6 6 Plants'- 



5 5 5 4 5 5 29 

 1/2 3 3 3 2 2 2 15 



1 2 2 2 2 2 1 11 



2 2 112 12 9 

 4 10 11 3 

 8 000000 



° See text for description of stages of development. 



*■ Called relative stage of floral development in Tables IV to VII. 



these stages the involucral bracts of the inflorescence were present, 

 and at the time of dissection they enveloped the receptacle. 



Irradiation of plants for half a minute in the middle of each 15-hr 

 dark period with light from the red source reduced flower formation to 

 stage 2 (terminal just starting to become capitate and very few bract 

 primordia present) or stage 3 (terminal clearly capitate and 12 or 

 more bracts present). Complete vegetativeness of all plants (stage 0) 

 resulted from 8 -min treatments and almost complete vegetativeness 

 (stage 1, terminal meristem elevated higher than in vegetative plants 

 but not yet starting to become capitate) from 4-min treatments. The 

 effectiveness of light from the red source varied slightly in successive 

 experiments, but usually 4 min was adequate to prevent initiation of 

 flower primordia. 



Repromotion of Flowering in Chrysanthemum by Far Red 



In a typical experiment flowering of chrysanthemums, which was 

 completely inhibited by 9 min of red light, was repromoted by 1 min 

 of far red (Table III). The far-red source consisted of three 300-watt 

 internal-reflector tungsten-filament lamps mounted about 50 cm apart 

 and about a meter from the plants. Radiant energy from this source 

 was filtered through two layers each of blue and red cellophane. In 

 this particular experiment 3 min of far red had as strong a repromotive 

 effect on flowering as 9 min and only slightly more than 1 min. The 

 flowering stage attained by repromotion with far red was appreciably 

 less advanced than that of the controls in this experiment and in many 

 others done with the same (Table IV) or similar varieties. 



