GROWTH REGULATORS AND COCKLEBUR FLOWERING 391 



3. That is, light interruption is approximately equivalent to returning 

 plants to light (the critical night has been extended for cobaltous- 

 treated plants). The processes that go on during the first part of the 

 dark period, however, appear to be slowed down by the presence of 

 cobaltous ion. Indeed, this would account for the increase in the criti- 

 cal night length and the inhibitory effect of cobaltous ion. 



At this stage of the investigation, since the saturating quantity of 

 light appears to be the same with or without cobaltous ion, it appears 

 that pigment conversion is not influenced by the cobaltous ion, but that 

 the preparatory reaction is in some manner decreased in velocity. 



Work is also being carried on with gibberellic acid, although at this 

 stage of the investigation, this work has all been of a preliminary 

 nature. 



In addition to the studies of growth regulators which are known to 

 influence the flowering process, a continual effort is being made to dis- 

 cover new compounds which will influence the flowering process and 

 allow us to gain further insight into the steps and mechanisms of this 

 natural phenomenon. 



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Downs, R. J. 1956. Photoreversibility of flower initiation. Plant Physiol., 31, 

 279-83. 



Hamner, K. C. 1940. Interrelation of light and darkness in photoperiodic induc- 

 tion. Botan. Gaz., 101, 658-87. 



Khudairi. Abdul-Karim. and K. C. Hamner. 1954. The relative sensitivity of 

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Liverman, J. L. 1955. The physiology of flowering. Ann. Rev. Plant Physiol., 6, 

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Liverman, J. L., and J. Bonner. 1953. Biochemistry of the photoperiodic 

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Lockhart, James A.T and Karl Hamner. 1954. Partial reactions in the formation 

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Mann, Louis K. 1940. Effect of some environmental factors on floral initiation 

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Salisbury, F. B. 1955. The dual role of auxin in flowering. Plant Physiol., 30, 

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