352 GROWTH FACTORS AND FLOWERING 



During some preliminary observations of flowering phenomena, we 

 noted that here again the action of GA resembles in certain cases that 

 of far-red irradiation. In fact, there are LDP whicli react to GA in 

 short-day conditions as they do in short-day plus far-red extension 

 (9 + 15 hr). We received the impression, moreover, that this reaction 

 to GA was not manifested by plants that react positively, with respect 

 to flowering, to red light extension (Lona, 1957a). 



Successive experiments, however, did not yield such clear-cut re- 

 sults. GA action on the flowering process did not always appear similar 

 to that of far red, and moreover it seemed, in a few rosette plants, to 

 substitute somehow for the red, perhaps also independently from their 

 flowering processes. After these conflicting results, the interest in 

 comparing light and GA action still remained very strong and also 

 more stimulating. Therefore we continued our tests on these lines. 



Realizing that knowledge of the reaction of our test plants to 

 duration and quality of supplementary light was incomplete, it was nec- 

 essary to go deeper and more precisely into the question of the specific 

 ways in which different plants (even of the classical categories) react 

 to various types of long day. 



A set of trials on the effect of light extension to a basic short day, on 

 certain LDP, concerned red and far-red light of the standard type at 

 low energy (1 kiloerg/cm--sec) and at temperatures ranging from 

 18° to 22 °C. The few data available at present concern not only 

 flowering but also stem growth in the photoperiodic picture. It is 

 convenient from certain points of view to treat the two subjects in 

 parallel, trying to distinguish the direct action of the external factors 

 of the two phenomena and, possibly, avoiding eventual confusion due 

 to some reciprocal influence between them. It will be particularly use- 

 ful to ascertain how differently growth and flowering depend on the 

 quality of light applied during the scotophil phase. 



Experimenting with the following three different photoperiod con- 

 ditions, i.e., (a) 8 hr natural light + 16 hr dark (SD), (b) 8 hr 

 natural light -f 8 hr red light + 8 hr dark (rLD), or (c) 8 hr natural 

 light + 8 hr far-red light + 8 hr dark (f-rLD), we could distinguish a 

 series of reaction types. One example is Centaurea cyan us. It flowers 

 quickly when the long day is obtained through red light extension, 

 whereas under a far-red extension its flowering behavior appears sim- 



