58 THE FLOWERING PROCESS 



three, the gibberellins are by far the most important, and it is possible 

 that more detailed work could expand the gibberellin class to include 

 the other two. 



1. The Soak Water from Vernalizing Seeds 



Harry Highkin (51) at the California Institute of Technology at 

 Pasadena was able to speed up the flowering of certain pea varieties 

 by treating the germinating seeds with low temperature. He then 

 applied the water, which contained materials that had diff'used out 

 of the vernalizing seeds, to unvernalized pea seeds, or even to Petkus 

 rye seeds, causing these plants to flower sooner. Gregory had 

 obtained similar results years before with the soak water from 

 vernalizing rye seeds, but his work was not continued. This work is 

 of interest for two reasons : first, the extractions were made in direct 

 connection with the vernalizing process, and second, preliminary 

 analyses of Highkin's extract seemed to indicate that the active 

 principle was a nucleotide. Furthermore, ribonucleic acid (RNA) 

 has been reported to promote flowering of cold requiring plants. 

 In a morphogenetic process such as flowering, the nucleic acids must 

 participate, if only in the cell division phase of the process, and any 

 evidence which implies that they might be active in other steps of 

 the sequence of events must be viewed with interest. 



2. The Gibberellins (56) 



These compounds, originally extracted from a fungus, have been 

 investigated very extensively during the past decade for their eff^ects 

 upon higher plants. The most common observation is that they are 

 powerful promoters of stem elongation. Although there is usually 

 no increase in dry weight of the plant, the stems may elongate up to 

 six times as fast after gibberellin treatment, and in some cases such 

 as rosette plants, treatment may cause elongation where none would 

 have occurred otherwise. 



It was discovered at an early stage of the research that some plants 

 which normally require cold treatment or long days for flowering 

 will flower under non-inductive conditions when they are treated 

 with gibberellins (see Fig. 4-3). The response is widespread but of 

 course varies considerably from species to species. As a rule repeated, 

 substantial doses are required. For example, with Samolus parviflorus 

 a total of 20 micrograms (1 /xg/day for 20 days) was very effective, 



