FLOWERING HORMONE MOVEMENT AND ACTION 195 



the leaves have received the inductive dark period. Apparently the 

 hormone disappears if it doesn't find an active bud within that time, 

 and leaves lose their ability to produce it. As a matter of fact, plants 

 with developing flowers will revert to the vegetative condition if all 

 the active buds are removed. 



This is not true in the case of Perilla. Leaves detached from the 

 plant can be induced and kept for many weeks until they finally die 

 without losing their ability to cause a vegetative plant to become 

 reproductive when they are grafted onto it. But then Perilla differs 

 from cocklebur in that leaves can only become induced by the 

 environment and not by other leaves on the plant. 



Obviously there is a great deal more to be done along these lines. 

 Again it seems quite clear that the real problem is concerned with the 

 biochemical nature of the flowering substance itself. We need to 

 know how it is synthesized in the first place. What is its condition 

 while it is being translocated? How is it maintained in the plant? 

 Does it remain the same or is it changed in some way in the bud ? 

 How does it move into young cocklebur leaves, making them 

 capable of inducing receptor plants ? Why does this fail in Perilla ? 

 Why does it disappear in the cocklebur when there are no active buds ? 



Applied auxins or gibberellins, or the presence of very young leaves 

 will retard or prevent this disappearance in the absence of active buds. 

 In the last chapter we concluded that auxin in the leaves may destroy 

 flowering hormone; now it appears that auxin in the buds prevents 

 the destruction of flowering hormone or gives the bud the ability to 

 produce it continually. Does this mean that auxin acts differently in 

 the two tissues or that the hormone from the leaf is changed after it 

 gets to the bud ? 



It should now be clear that flowering, in common with plant 

 growth phenomena in general, is influenced to a very significant 

 extent by growth regulators such as the auxins and gibberellins. One 

 of the primary problems of future flowering research is to elucidate 

 these influences. Some initial work has been concerned with simply 

 trying to measure the growth regulator status of plants under different 

 environmental conditions. The approach is to extract tissue with 

 suitable solvents, and then to test the extracts in various bioassays. 

 Growth promoter activity is often tested using oat coleoptile curvature 

 or elongation tests, split pea stem tests, etc. Presence of gibberellins 

 is indicated by effects upon dwarf mutants such as those of maize. 



