110 • Chemical Control of Flowering 



under long days in experiments by Bonner and Bonner (1948). 

 Unfortunately their attempts to repeat this work, with inflorescence 

 extracts from the same and other species of palm, were completely 

 unsuccessful, so the result remains unexplained. 



In 1951, Roberts also reported the extraction of a substance that 

 induced flowering in Xanthium under long days. It appeared to be 

 of a lipide nature and obtainable only from flowering, not vegeta- 

 tive, individuals of a number of species including Xanthium itself. 

 Although attempts in several other laboratories have failed to con- 

 firm Roberts's results, a long-chain keto-alcohol with activity as an 

 auxin antagonist can be prepared from certain plants by the pro- 

 cedures used (see Struckmeyer and Roberts, 1955). Its florigenic 

 properties, however, remain as doubtful as those of the palm extract. 

 An extract with weak but significant flower-promoting activity for 

 Xanthium plants in long days has recently been prepared by 

 careful lyophilization of Xanthium inflorescences. Only future 

 work will decide whether this result will go the way of the others 

 cited, but the initial report is very encouraging (Lincoln et a\., 

 1961). 



In an extensive investigation on the development of a straw- 

 berry (Fragaria) variety, Sironval (1957) has reported that unsaponi- 

 fiable lipide fractions from flowering plants promote flowering of 

 those in the vegetative condition. In only a few experiments, how- 

 ever, are the untreated controls completely vegetative, and often 

 the differences between control and treated series are discouragingly 

 small. The active substances in the extracts may include Vitamin E, 

 which is itself active in the strawberry-plant test, and certain uni- 

 dentified sterols. 



Flowering in at least one vernalizable variety of pea (Pisum 

 sativum) can be promoted by first allowing the seeds to imbibe 

 "diffusate" prepared from other pea seeds (Highkin, 1955). Like 

 vernalization, such treatment results in flowering at a lower node 

 than in the controls; in the data published, the node number to 

 the first flower was about 20 in the controls to about 18 in the 

 treated, but was highly significant statistically. By a "diffusate" is 

 meant an extract prepared not by grinding seeds in water but 

 simply by soaking them, intact, under sterile conditions for varying 

 periods of time during which active substances diffuse out into the 

 water. Such diffusates probably contain many metabolically impor- 



