120 



THE FLOWERING PROCESS 



5 10 15 20 25 30 



MINUTES OF DARKNESS BETWEEN RED AND FAR-RED 



Figure 7-9 

 The effects of far-red light (3 min) given at various times after interrup- 

 tions with red (2 min) given near the middle of three 12-hr dark periods. 

 Data from R. J. Downs, 1956, Plant Physiol 31, 279-284. The 

 flowering stages of Downs have been converted according to his des- 

 cription to the Floral Stages described in Chapter 5. 



Thus it appears that in cocklebur F-phytochrome completes its 

 inhibitory act in 30 min. In chrysanthemum, however, 4 hr is required 

 for complete inhibition, and F-phytochrome decays to R-phyto- 

 chrome in much less time than this (perhaps on the order of 30 min). 

 To inhibit flowering then, F-phytochrome must be available for 

 about 4 hr, and it can either be maintained continuously by constant 

 light, or it can be renewed at regular intervals by repeated light 

 interruptions. 



6. The Phytochrome System in Japanese Morning Glory (32) 



Although there is ample evidence that phytochrome plays an 

 important part in flowering of Japanese morning glory, it appears 

 from the extensive and detailed work of the Japanese, and recently 

 the Beltsville team, that its specific role is clearly quite diff'erent from 

 the role played in the cocklebur. The story becomes quite involved, 

 and the interested reader is referred to the many original papers. 

 Here are some of the basic facts. 



