94 • Floral Hormones and the Induced State 



CONCLUDING REMARKS 



An attempt at some sort of evaluation is desirable here, if only 

 to avoid ending on a note of complete confusion. Some of the views 

 to be expressed differ greatly from those held by other writers, who 

 also differ among themselves; anyone seriously concerned with 

 theoretical interpretations should consult various reviews cited 

 earlier. 



The "all-or-none," qualitative character of both floral initia- 

 tion and photoperiodic induction has been widely stressed (for 

 example, Lang, 1952). In the writer's opinion, it is a questionable 

 concept. Admittedly, there are situations in which one either sees 

 or does not see a floral primordium, so that the final judgment is 

 either "flowering" or "vegetative." The same could be said, how- 

 ever, about the growth or nongrowth of a piece of tissue; at the 

 lower limit of the technique used, one either detects growth or 

 does not, yet there is no general opinion that growth is an all-or- 

 none phenomenon. Bonner (1959a), accepting the photoperiodic 

 response as in a sense quantitative, nevertheless goes on, "each 

 bud and each plant is either reproductive or vegetative." Logically, 

 this is true enough. But in developmental, morphological terms, 

 one has only to consider work like that of Harder (1948) on 

 Kalanctwe to reali/e that there can be a continuum between obvi- 

 ously vegetative and obviously reproductive growth. 



One origin of the all-or-none view may be an overemphasis 

 on flower initiation (although such studies usually involve some 

 degree of development) with too little attention to the fact that 

 optimum flower development often requires a continuation of the 

 inducing conditions. A good illustration of this common situation 

 was recently given by Zabka (1961) working with Amaranth us 

 raudatits. At a certain age this is a very sensitive SDP; when older, 

 it initiates flowers even under long days. Under any circumstances, 

 however, inflorescence development and fruiting are strongly 

 favored by short days, no matter how initiation came about. 



Another major support of the all-or-none view has been the 

 fact that, in SDP lor example, flowering does not occur at day- 

 lengths above the critical but does occur at lower values. This thus 

 n( emed to represent a sharp, qualitative cut-oil in the curve of 



