NOTE ADDED IN PROOF 217 



Discussion with G. Meijer at Eindhoven in Holland convinced me 

 that I have previously interpreted his results incorrectly (see p. 123). 

 Rather than contradicting the results of W. Konitz, his experiments 

 collectively seem to support the idea that far-red light will act in an 

 inhibitory way when it is given during the main hght period (see also 

 below). 



Many of the experiments listed as being unpublished will appear 

 in three technical papers in the journal Planta almost concurrently 

 with the pubhcation of this book. These include the experiment of 

 Figs. 3-7, 7-8, 8-5, 8-6, 9-2, 9-5, 9-6, 9-7, 9-8, 9-13, and 9-15, 

 Table 9-1, and the cobaltous ion results mentioned on pp. 142-3. 



Some of the experiments which we have been performing in recent 

 months on Timing and the High Intensity Light Process provide 

 answers to certain of the questions raised in the text. To begin with, 

 the inhibitory effect of a red light interruption given 8 hr after the 

 beginning of the dark period cannot be reversed by application of 

 sucrose, even though this interruption is followed by 12 hr or more 

 of hght (see pp. 117, 135, and 142). Thus, although ample sugar is 

 present, the clock which measures the dark period will not restart 

 after such an interruption. Why, then, did the experiment of 

 Liverman and Bonner (p. 98) succeed? Probably because they gave 

 24 hr of flashing light, which might allow the clock to make a com- 

 plete cycle and be back at its starting position, after which the 

 sucrose depleted during the 24 hr of flashing Hght might indeed be 

 limiting. We have tested this explanation with one prehminary 

 experiment. Apphed sucrose essentially failed to make a long dark 

 period effective after only 8 hr of flashing hght but partially succeeded 

 after 16 hr of flashing hght and succeeded quite well after 24 hr of 

 flashing Hght ! This is strong evidence in favor of an oscillating timer 

 which times the dark period in the flowering process of cocklebur. 



We have wondered how much Hght might be required to start the 

 clock following a Hght interruption 8 hr after beginning of the dark 

 period. To find out, we exposed cocklebur plants to 8 hr dark (or 

 Japanese morning glory to 10 hr dark — the critical night length), 

 then to different durations of Hght in the growth chamber, and then 

 to a long inductive dark period (12 hr with cocklebur, 18 hr with 

 Japanese morning glory). For the first hour or two, flowering is 

 inhibited, but after 8 hr of light (both plants) the level of flowering 

 reaches that of uninterrupted controls. Since sucrose fails to replace 



