INFLUENCE OF CERTAIN GROWTH REGULATORS 

 ON FLOWERING OF THE COCKLEBUR 



FRANK B. SALISBURY 



Department of Botany and Plant Pathology, Colorado State University, 



Fort Collins 



THE PARTIAL PROCESSES 



The flowering process, especially as it applies to the cocklebur 

 {Xanthium pensylvanicum Wall.), has been divided into a series of 

 partial or component processes (Liverman, 1955; Salisbury, 1957b, 

 1958; Salisbury and Bonner, 1956). This division into steps has served 

 as a framework of reference for evaluation of experiments done with 

 short-day plants and has in some cases suggested new approaches to 

 the problem of flowering. Since this system of partial processes has 

 served as a foundation for the experimental work presented in this 

 paper, it is summarized below as it appHes to cocklebur, 



High-Intensity Light Process 



The experiments of Hamner (1940) and those of Liverman and 

 Bonner (1953) indicated that the inductive dark period was ineffective 

 unless sufficient photosynthates have been produced during the preced- 

 ing light period. It is possible that the high-intensity light requirement 

 involves more than photosynthesis (Lang, personal communication), 

 but at present the more subtle aspects of this partial process remain 

 vague. 



Reactions of the Dark Period 



1. Pigment Conversion. It has been suggested by Borthwick and 

 co-workers (1952) that a reversible photoreceptor pigment exists in 

 the leaf of plants sensitive to photoperiod, and that this pigment must 

 be spontaneously converted from a far-red-receptive form to a red- 

 receptive form before other reactions of the dark period may proceed. 

 It has further been suggested (Salisbury and Bonner, 1956) that the 



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