Figure I. Tips of cocklebur plants with older leaves removed. A, Non- 

 flowering plant. B, Fruiting plant (induced by short days). C, Partial fruiting 

 induced by one long dark period. D, Nearlv normal fruiting induced by plant 

 extract in addition to one long dark period. E, Partial truiting trom two long 

 dark periods. F, Partial fruiting following treatment with plant extract. 



