82 • Floral Hormones and the Induced State 



and flower-inhibiting substances both play a part in these effects, 

 but their nature is unknown. 



Resentle (1959) also supports the concept that flowering 

 generally depends on a change in a complex balance rather than 

 on either simple flower-promoting or flower-inhibiting substances, 

 since his experiments with the Crassulaceae (Bryophyllum, 

 Kalanchoe, Bryokalanchoe species) have indicated all degrees of 

 transfer of the "floral state" or "vegetative state" from one plant to 

 another by grafting. Further discussion on the merits of various 

 hypotheses will be deferred until the concluding section of the 

 chapter. 



VERXALIN AND METAPLASIN 



In addition to florigen and flowering inhibitors, the participa- 

 tion of other transmissible substances in flowering or processes 

 related to it has been suggested. With regard to vernalization, 

 Melchers (see Melchers and Lang, 1948; Lang, 1952) has assumed 

 the existence of a substance called "vernalin" on the basis of 

 experiments with biennial Hyoscyamus. If two of these Hyoscyamus, 

 one previously vernalized and one unvernalized, are grafted 

 together, both will flower in response to long days, although an 

 unvernalized plant alone will not. This might indeed be due to 

 transfer of vernalin from the vernalized to the unvernalized plant, 

 but it can be equally interpreted as a movement of floral stimulus 

 from the vernalized, long-day treated plant to the other that, 

 unvernalized, cannot respond to long days. The "vernalin" inter- 

 pretation is based on the additional observation that unvernalized 

 biennial Hyoscyamus grafted to Maryland Mammoth tobacco will 

 flower in long days, in which the tobacco itself is not induced. 

 The tobacco is visualized as a donor of vernalin— produced without 

 vernalization in a non-cold-requiring plant— enabling the unver- 

 nalized biennial to respond to long days. In this view, vernalin 

 is either a direct biochemical precursor of florigen or makes its 

 synthesis possible. 



The difficulties of interpreting grafting experiments with 

 tobacco (Nicotiana) species, some of which were mentioned 

 earlier, make this evidence less than completely convincing. To 

 the writer's knowledge, there has never been any clear demonstra- 



