358 GROWTH FACTORS AND FLOWERING 



(for extension of blue light) and, moreover, the light conditions of 

 the photophase. The rhythmical different exigencies of light in con- 

 nection with endogenous rhythm and sensitivity appear to be of funda- 

 mental importance for distinguishing the different processes leading to 

 growth and flowering. 



When the specific environmental exigencies of every single phenom- 

 enon (growth, flowering, seed germination, etc.) are clearly discerni- 

 ble so as to discriminate their particular mode of initial reaction to 

 external stimuli and their successive processes, which are also evidently 

 different, we shall be able to understand the true significance of the 

 various physiologically active substances on the plant. The very con- 

 sistent differences between the modalities of response to light by 

 flowering processes and those of growth should be studied also ac- 

 cording to cytological manifestations distinguishing cell elongation 

 and cell reproduction. 



REFERENCES 



Downs, R. J. 1956. Photoreversibility of flower initiation. Plant Physiol., 31, 

 279-84. 



Lang. A. 1956. Induction of flower formation in biennial Hyoscyamus by treat- 

 ment with gibberellin. N aturwissenschaften, 43, 284-85. 



Livermann, J. L. 1955. The physiology of flowering. Ann. Rev. Plant Physiol., 

 6, 177-210. 



Lona, F. 1956a. L'acido gibberellico determina la germinazione dei semi di 

 Lactuca scariola in fase di scoto-inibizione. Ateneo parmense, 27, 641-44. 



. 1956b. Osservazioni orientative circa I'effetto dell'acido gibberellico 



sullo sviluppo riproduttivo di alcune longidiurne e brevidiurne. Ateneo 

 parmense, 27, 867-75. 



1957a. Vegetative and developmental manifestations of some plants 



in connection with gibbereUin compounds activity. Abstract from the lecture 



given at the University of Wageningen on May 23, 1957. 

 Lona, F. 1957b. Brief accounts on the physiological activity of gibbereUic acid 



and other substances in relation to photothermal conditions. CoUoque Int. 



sur le photo- et thermoperiodism, etc. (Parma, June 1957). Bull. No. 34 



I UBS, ser. B. 

 Lona, F., and Ada Bocchi. 1956. Interferenza deU'acido gibberellico nell'effetto 



della luce rossa e rosso-estrema suH'allungamento del fusto di Perilla ocy- 



moides L. Ateneo parmense, 27, 645-49. 

 Stolwijk, J. A. J., and J. A. D. Zeevaart. 1955. Wavelength dependence of 



different Hght reactions governing flowering in Hyoscyamus niger. Proc. Ned. 



Akad. Wetenschap., C58, 386-96. 



