The Biochemistry of Induction • 91 



Overbeek and Cruzado, 1948). In certain soybean varieties also, 

 keeping the stem apex bent over causes earlier flowering, which 

 Fisher (1957) again attributes to auxin redistribution, presumably 

 a lower level at the older nodes resulting from an accumulation at 

 the apex. 



Hypotheses on the role of auxin in flowering have been based 

 largely on the effects of externally applied auxins and related 

 compounds, to be considered in the next chapter, rather than on 

 the kind of work described above. Neither type of evidence has 

 lent itself to any simple interpretation. In addition to hypotheses 

 in which auxin simply inhibits or promotes flowering, one of the 

 most elaborate schemes suggested relates its action directly to the 

 red, far-red reversible system (see Liverman, 1955). The evidence 

 is derived largely from work with processes other than flowering, 

 and the "morphogenetic photocycle," as the scheme has been called, 

 has not been widely accepted, at least in its original form (see Lang, 

 1959; Hillman, 1959c). 



The gibberellins, a class of compounds to be discussed in the 

 next chapter, can cause flowering in many LDP when applied 

 externally. So far there is little information on whether the control 

 of the level of these substances by photoperiod or temperature may 

 explain certain flowering responses. Some of the Harada and Nitsch 

 (1959) results are suggestive of a change in gibberellin levels follow- 

 ing induction, but the bioassay used was relatively unspecific. A- 

 more specific assay was used by Lang (1960), whose preliminary 

 results show a higher gibberellin level in induced than in non- 

 induced annual Hyoscyamus. That this may be a cause of flowering 

 rather than simply correlated with it is indicated by the fact that 

 the increase shows up soon after induction and is less pronounced 

 after flowering is well under way. This sort of work is now develop- 

 ing rapidly; and, as mentioned earlier about research on the 

 red, far-red pigment, what is reported here may well be obsolete 

 by publication. 



The role of respiratory systems has also been studied. Elliott 

 and Leopold (1952), for example, following oxygen uptake in leaf 

 tissues of certain SDP and LDP, concluded that respiration rate 

 increased in the former and decreased in the latter with photo- 

 induction, whereas rates in two daylength-indiflerent plants were 

 dependent on the total light given. Whether such correlations are 



