98 THE FLOWERING PROCESS 



the short dark periods, then the subsequent long dark period was 

 effective and the plants flowered. This is illustrated in Fig. 6-1. 



The experiment is easily interpreted assuming that effectiveness 

 of the long dark period depends upon the presence of sugars or other 

 energy sources which are produced by photosynthesis and used up 



HOURS BEFORE OR AFTER BEGINNING OF THE INDUCTIVE DARK PERIOD 



36 24 12 12 



1 \ \ \ \ \ 1 \ 1 



HmHiHHH 6-0 

 Hamner's experiments: 



^■— ^— 4-8 



Indicates a 3 minute ^^^^ ^^^^^^^^ 



light interruption ^■■■■^■^■^^^^^■■i 0-0 



_^_»i..».i.....»__ 00 I 



Sunlight ^■ 



^"■^— ■""■■" ■" ^-=— =~^ 3-3 "> 



Sunlight ::5 



^■■— ^^"M^^— i— ■■^i«= 6-0 o 



Sunlight n 



10 ft-c. "^ 



100 ft-c 



24 ^ 12 ^ 24 



Liverman and"* ' ' ' ^TZZITTTTZ ' 



Bonner^s "-"^"^^ '" °"^ 



experiment: Sunlight Leaves in oir 



Leaves submerged in water 



Leaves submerged in 1% sucrose solution 

 i^^^Bi.^.a...a^UiiiiiMiiiiiiilMMiiiiiiltiMMIH 44% 



Figure 6-1 

 Some of the experiments of K. C. Hamner (Botan. Gaz. 101, 658-687, 

 1940) showing the effects on flowering of cocklebur of intermittent light 

 and dark periods and other treatments preceding a dark period of 

 normally inductive length ; and experiments of J. Liverman and J. Bonner 

 {Botan. Gaz. 115, 121-128, 1953) showing eff"ects of sugar applied during 

 a long dark period which has been preceded by intermittent light and 

 dark periods. It was possible to convert Hamner's flowering data 

 roughly to the Floral Stage system described in Chapter 5. Liverman 

 and Bonner present only data for the per cent of the treated plants which 

 flowered. Before and after treatment, plants were subjected to long days 

 in the greenhouse. Buds were examined after 3 weeks. Solutions were 

 applied by immersing the leaf in the solution during the entire inductive 

 dark period. In other experiments solutions were applied by putting 

 cuttings into the solution at the beginning of the long dark period. Three 

 minute light interruptions were 200 ft-c (Hamner) or 50 ft-c (Liverman 

 and Bonner). 



