282 CONTROL OF REPRODUCTION 



Table V. Repromotion of Floral Initiation in Several Early-Flowering Varieties of 

 Chrysanthemum by Far Red Given Immediately after Red 



Relative Stage of Floral Development" 



" Values represent totals for 3 plants adjusted to basis of 6 plants for comparison with 

 other tables. See text for description of stages of development. 



Far-red repromotion of flowering of coclclebur resembles that of 

 these early chrysanthemum varieties in that the flower primordia of 

 the reinduced plants usually develop almost as well as those of the 

 unirradiated controls (Downs, 1956). Far red almost always repro- 

 motes flowering of all plants of Indianapohs Yellow, Shasta, and cer- 

 tain other varieties, but the primordia are almost invariably less 

 advanced than those of the controls. Repromotion of flowering by far 

 red often fails in lamb's-quarters (Chenopodium album L.) and when 

 it succeeds, the flower primordia are not well developed. 



Repromotion of Flowering by Far Red Dependent on Time 

 between Red and Far-Red Treatments 



The maximum degree of repromotion of flowering attainable in 

 various kinds of chrysanthemums with far-red treatments usually 

 occurs when treatments of about 1 to 1 min are given as quickly as 

 possible after the red treatment. If the time between red and far-red 

 treatments exceeds about 45 min, the effectiveness of the far red in 

 repromoting flowering decreases, and if it is as much as 90 min, re- 

 promotion of flowering often fails completely (Table VI). 



This effect was observed first in cocklebur (Downs, 1956), in 

 which repromotion of flowering failed in about 30 min. The red light 

 apparently forms a product, the far-red-absorbing form of the pigment, 

 which in short-day plants such as cocklebur and chrysanthemum starts 

 reactions that lead to prevention of flowering. If these reactions are 

 permitted to run a sufficient part of their course, flowering will ob- 



