PHOTOPERIODISM IN SEEDS AND BUDS 



83 



presence of growth inhibitors has been put forward by Hemberg 

 (1949) and others. It is possible, therefore, that the formation of 

 resting buds in response to short days may be due to the production of 

 greater amounts of a growth inhibitor under short days than under 

 long days. We have carried out investigations to test this hypothesis 

 using primarily Acer pseiidoplataims (Phillips and Wareing, 1958). 

 Preliminary experiments showed that there is an inhibitor in the 

 leaves and buds of A . pseudoplatcmus which is completely extractable 

 with 80% aqueous methanol. After extracting the tissues with this 

 solvent, the extracts were partitioned by paper chromatography by 

 using a running solvent consisting of 80 parts isopropanol to 20 parts 

 aqueous ammonia (0.88 S.G. x Moo)- After development the chroma- 

 tograms were eluted in water and assayed for growth activity by using 

 primarily the wheat coleoptile section test. The growth inhibitor was 

 found to occur between Rf 0.6 and 0.8. A study was made of the 



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LONG DAY 



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SHORT DAY 



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Fig. 2. Assay with wheat coleoptile sections of chromatographed ex- 

 tracts (each equivalent to 0.1 g dry weight of tissue) of mature leaves. 



