Plant Extracts of Various Kinds • 109 



threshold conditions just as do several auxins. No convincing 

 hypothesis about such results has yet been stated (see Lang, 1959). 



Many growth regulators can speed or delay flowering some- 

 what under particular circumstances. These effects are usually 

 minor and are also associated with equal or greater effects on 

 vegetative growth. Occasionally, dramatic and at present inexpli- 

 cable effects of particular compounds on particular plants are discov- 

 ered, of which two examples will be cited. For further information, 

 see Audus (1959) and Leopold (1958). 



Furfuryl alcohol, a compound not previously known to have 

 growth-regulating activity for higher plants and not obviously 

 related to known growth regulators, promotes flowering and bolting 

 in the LDP Rudbeckia speciosa under short days in the same way 

 as does gibberellin (Nitsch and Harada, 1958). In one of the two 

 experiments reported, some of the control plants flowered as well, 

 so the conditions may have been close to threshold. Effects on other 

 plants are unknown. 



The compound N-metatolylphthalamic acid is one of a group 

 of growth regulators that profoundly affects flowering as well as 

 other processes in a number of plants. It is particularly effective in 

 increasing flowering in the tomato {Ly coper sicon esculentiim), a 

 daylength-indifferent plant, chiefly by increasing the number of 

 flowers in each cluster. High doses may even cause the development 

 of a large inflorescence at the apex, causing further vegetative 

 growth to stop. Such promotions of inflorescence development 

 appear to be due to temporary or permanent suppression of the 

 branch that would otherwise arise beneath an inflorescence and 

 compete with it, and are almost certainly not direct effects on 

 flower initiation (Cordner and Hedges, 1959). 



PLANT EXTRACTS OF VARIOUS KINDS 



Many naturally occurring substances have been tested for 

 possible flower-promoting activity, often as extracts of uncertain 

 composition. No such work, other than that with gibberellins, has 

 as yet been conspicuously successful, but it is well to consider some 

 representative efforts. 



An extract of the young inflorescence of a palm, Washing- 

 tonia robusta, apparently brought about flowering in Xanthinm 



