A CORRELATION OF PHOTOPERIODIC RESPONSE 



OF Xanthium AND GERMINATION OF 



IMPLANTED LETTUCE SEED' 



LAWRENCE BOGORAD and WAYNE J. McILRATH 



Department of Botany, The University of Chicago, Chicago, Illinois 



Several of the papers presented at this symposium have reviewed and 

 documented the marked similarity in action spectra for a number of 

 responses; these include the control of photoperiodic induction of 

 floral initiation, germination of seeds of certain varieties of lettuce, leaf 

 expansion, and internodal elongation. The diversity in types of re- 

 sponses is evident. The present experiments were designed to investi- 

 gate the following problems: Does the similarity in these systems ex- 

 tend beyond the identity in photoreceptor, and does the photoreaction 

 (and some ensuing steps) in each of these systems lead to the produc- 

 tion of the same substance which, in each case, elicits a different and 

 specific response (Bogorad and Mcllrath, 1955; Mcllrath and Bogo- 

 rad, 1954; Mcllrath and Bogorad, 1958)? 



Lettuce seed germination and the photoperiodic control of floral 

 initiation, two well-characterized red, far-red reversible systems, were 

 chosen for investigation. The experimental approach was simple. When 

 Xanthium plants, grown in the greenhouse under a 20-hr photoperiod, 

 had reached a suitable size, slight incisions were made on the abaxial 

 surface of the petioles of the second, third, and fourth leaves from the 

 terminal bud. Up to about seventy dry lettuce seeds (achenes) were 

 implanted in each petiole. The petioles were then covered with either 

 a light-tight wrapper of aluminum foil (Fig. 1 ) or a transparent cover 

 of Saran Wrap (Dow Chemical Co.) (Fig. 2), sealed on with masking 

 tape (Minnesota Mining & Manufacturing Co.). The plants with im- 

 planted petioles were then subjected to various regimes of light and 



1 This investigation was supported in part by the National Science Foundation 

 (G-4018) and in part by the Dr. Wallace C. and Clara A. Abbott Memorial 

 Fund of the University of Chicago. 



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