178 THE FLOWERING PROCESS 



auxin concentrations within the leaf. Surely flowering must be 

 influenced by these changes, but at present it seems quite unlikely 

 that the act of induction is mediated through changes in endogenous 

 auxins. Applied auxins will inhibit flowering of cocklebur, provided 

 they are applied to the plant before the hormone is translocated out 

 of the leaf. What is the mechanism of this inhibition ? 



In explaining the results of the temperature experiment (Fig. 9-5), 

 we postulated a destruction or metabolic breakdown of flowering 

 hormone. Auxin might in some way accelerate this destructive 

 process. Since auxin is known to promote growth, it has been 

 suggested that the acceleration of flowering hormone disappearance 

 is simply a competition between energy requiring grov^h processes 

 and an energy requiring maintenance of flowering hormone (much 

 like the antagonism theory of flowering discussed in Chapter 4). 

 That is, if energy is continually required to keep the hormone from 

 disintegrating, then anything which would make it more difficult 

 for the leaf to use its energy in this way would result in a destruction 

 of flowering hormone. 



It also seems possible that auxin might simply stop (or severely 

 restrict) translocation of hormone from the leaf. The experiment 

 illustrated in Fig. 9-14 seems to indicate that this is not the case. A 

 translocation experiment of the type shown in Fig. 9-1 was per- 

 formed with control plants and with plants which had been treated 

 with auxin. Although flowering is inhibited, the basic time relation- 

 ships of flowering hormone translocation are not influenced. 



The quantities of auxin which are appHed to inhibit flowering of 

 cocklebur also cause vegetative responses. The leaves wrinkle and 

 the petioles twist and curl (epinasty). This in itself seems to indicate 

 (although it does not prove) that the auxin effects on flowering which 

 we observe in such experiments are not typical of the auxin effects 

 within untreated plants. 



Other compounds besides auxin act in the same way in the time 

 of application experiments (see Table 9-1). These include a number 

 of inhibitors of nucleic acid metabolism. At present we have no 

 suggestions about how these substances might act in flowering, but 

 the competition for energy idea as applied to auxin may also have 

 some merit here. 



