190 THE FLOWERING PROCESS 



the amount of flowering hormone reaching the bud is decreased. 

 This might be due to a requirement for sugar to stabilize the hormone, 

 prevent its destruction, or move it out of the leaf before it is destroyed. 



Induction and The Nature of Flowering Hormone 



(3, 14, 20, 25, 32, 38) 



The flowering hormone is exceptionally interesting in one respect : 

 once it is formed in certain plants it seems to catalyze its own 

 subsequent, further synthesis. This is beautifully illustrated by the 

 cocklebur, which changes from the vegetative to the reproductive 

 condition after a single inductive dark period. Furthermore, if a 

 young cocklebur plant is given one or a series of long dark periods 

 so that the plant becomes reproductive, the young leaves which grow 

 out in the weeks or even months to come are themselves capable of 

 causing flowering. These young leaves, which did not exist at the 

 time the plant initially received its long dark period (or were too 

 small to respond), can be grafted on to a vegetative plant which has 

 never been exposed to an inductive dark period, and they will cause 

 that plant to flower. Thus it appears that the flowering hormone is 

 not diluted out as the plant grows but seems to increase or grow 

 along with the plant. This is demonstrated in another way by passing 

 the flowering hormone through a number of graft "generations", as 

 mentioned in Chapter 9. We get the impression that flowering 

 hormone, once it has been synthesized within the plant, is continually 

 synthesized in all of the new cells that appear through the subsequent 

 growth processes. 



This is the sort of thing that the chemist calls autocatalysis, a not 

 unconmion chemical phenomenon. But in the case of autocatalysis 

 in which the presence of a molecule causes the further conversion of 

 precursor molecules into molecules like itself, it can be seen that the 

 end result will always be a maximum concentration of the auto- 

 catalytic molecule (see Fig. 10-3). Thus in autocatalysis the final 

 quantity of the product is not a function of the initial amount of this 

 material present but only of the precursor available for its synthesis. 

 Of course, the time required to reach the maximum amount will 

 depend upon how much of the original molecule was present, but 

 the final amount will not. 



