98 • Floral Hormones and the Induced State 



part of the plant, the leaf, is susceptible to modification by day- 

 length, there will be evidence of photoperiodically induced, trans- 

 locatable floral stimuli or inhibitors. When such production is not 

 under photoperiodic control, the stimuli or inhibitors may still 

 be demonstrable. There is no a priori reason to assume that these 

 are the same for all plants simply because they appear to be so 

 in certain closely related forms. (They do not appear to be so in 

 all: see Zeevaart, 1958.) On the other hand, work with the gib- 

 berellins indicates that the same compound can cause flowering 

 in many unrelated LDP, although gibberellins themselves cannot 

 be florigen, as will be indicated in the next chapter. 



The fact that floral stimuli to the present have proved non- 

 extractable, and are transferable only by grafting, has been used 

 as supporting evidence for the "virus" concept (see Bonner, 1959b) 

 in spite of the fact that many viruses are easily extracted and 

 transmitted by other means. It is at least as likely that the com- 

 pounds involved are simply unstable under most extraction tech- 

 niques. Still another possibility is precisely that florigen activity 

 is either due to a particular balance of substances or, as suggested 

 by Went (1959), is the reflection "of rhythmic concentration 

 changes" of one or more substances. In either case, extraction of 

 the right combination would prove extremely difficult, and move- 

 ment through a nonliving gap might disrupt the relationships 

 involved even though the substances themselves were stable. 



The reader may well protest that the intent of this section, 

 "to avoid ending on a note of complete confusion," has been badly 

 betrayed. In answer, the entire point here is that there is no con- 

 fusion, only ignorance. There are undoubtedly many growth- 

 regulating substances and systems of which we know nothing as yet, 

 and which will change present attitudes as much as work with the 

 red, far-red system or the gibberellins is changing those of the past 

 decades. Therefore a comprehensive statement on the subject of 

 this chapter is not only impossible but undesirable, since it would 

 have to assume that all parts of the puzzle are now in hand and 

 simply need putting together. All of the concepts in the literature 

 are valuable to the extent that they are useful as working 

 hypotheses, but they should not be mistaken lor anything else. 

 What we need is more of the missing pieces, wherever or however 

 thev mav be found. 



