PHOTOTHERMAL AND CHEMICAL CONTROL 357 



The second very significant factor for growth and flowering phe- 

 nomena is the influence of temperature. We know that night temper- 

 ature has an important role in the slow pigment conversion and con- 

 sequently in the whob reaction to photoperiod. Noteworthy is the fact 

 that temperature does act on growth in a simpler way than on flower- 

 ing. Liverman (1955) demonstrated that for the LDP Silene armeria, 

 the critical day length for flowering is shorter at 17° and 30°C (night 

 temperature) than at either 14° or 23°C. Liverman (1955) says: 

 "these results serve to point out that in experiments on the effect of 

 temperature on flowering response, it is necessary to use a number of 

 different temperatures in combination with a number of daylengths 

 to obtain results which are meaningful. [We can now suggest] a 

 number of different temperatures in combination with a number of 

 photochromoperiod conditions." In this way we may perhaps approach 

 a better understanding of the problems with which we have dealt 

 above. 



Again, simple relationships are likely to be found only between the 

 action of night temperature and that of GA in the sector of growth 

 manifestations (Lona, 1957b). Probably we cannot say the same 

 thing in regard to flowering; this problem, however, is rather un- 

 explored and we are now beginning some trials on it. 



As far as the vernalization phenomena are concerned, Lang (1956) 

 found a similarity of action between GA and a long treatment with 

 low temperature leading to flower formation. This homology does not 

 appear to be constant. 



In conclusion we observe that the actual experimental evidence 

 allows us to foresee the points of contact between the action of several 

 external factors on the primary receptive systems and related secondary 

 processes with that of GA. Consequently GA-like substances of the 

 plant may find their places in the near future inside the schemes of the 

 various processes of growth and developmental phenomena. Other 

 substances of primary importance in these schemes would be kinetin or 

 kinetin-like substances and the auxins such as lAA and other indole 

 compounds (Lona, 1957b). For a more precise understanding of 

 these relationships, further investigations should encompass a broader 

 variety of light and temperature conditions to include varying duration 

 and intensity of supplementary light as well as different wavelengths 



