LIGHT AND THE PIGMENT 123 



least as long as 775 m/z, becoming more important at shorter wave- 

 lengths. Incidentally, the experiment can be interpreted in another 

 way using the High Energy Reaction of Mohr. 



8. Some Other Light Responses (7, 32) 



The literature is replete with studies on the light responses in 

 flowering of both long- and short-day plants. To try to review all 

 of this work here would produce a mass of disjointed narrative which 

 could serve little purpose in a book such as this. The facts are simply 

 not yet all in, and no one has yet been able to produce a comprehen- 

 sive and coherent picture which will explain in a biochemical and 

 photochemical way all of the reported observations. Nevertheless, 

 some of the phenomena are quite striking, and they certainly further 

 illustrate the breadth of the subject matter. A few examples follow. 



Light quality studies, using colored filters and sometimes more 

 elaborate apparatus, have been performed by a number of European 

 workers. Walter Konitz at Tubingen, Germany, found, for example, 

 that far-red light applied during the light period mhihiitd the flowering 

 of pigweed. Of course red light during the dark period also inhibited. 

 The response is a striking one of considerable significance. The far- 

 red eff'ect was reversed by red light — an observation which makes 

 it very difficult to understand how the phenomenon could have been 

 observed in the first place, since plants given far-red light were then 

 returned to white fluorescent light, very rich in red but lacking far-red. 

 G. Meijer on the other hand, found that far-red or blue given during 

 the light period inhibited flowering of Salvia occidentalism also a 

 short-day plant. J. A. J. Stolwijk and J. A. D. Zeevaart found the 

 same thing for the long-day plant Hyoscyamus. Obviously it is 

 difficult to know what to make of such opposite results. Another 

 example of these perplexing light quality studies is that of Meijer 

 who showed with Salvia that the proper mixture of wavelengths 

 during the light period allows red light during the dark period to 

 promote rather than to inhibit, thus in a sense converting it from a 

 short-day to a long-day plant! 



Somewhat more clear cut are the studies on whether incandescent 

 or fluorescent light is best for extending the day to promote flowering 

 of long-day plants. With many species, studied by a number of 

 workers, incandescent light seems to be best. As mentioned in Chapter 



