CORRELATION OF Xanthiiim AND LETTUCE SEED 



303 



Fig. 3. Germination of Grand Rapids lettuce seeds implanted under 

 light-tight aluminum foil wrappers in the petioles of Xanthium plants 

 maintained on 8-hr (above) and 20-hr (below) photoperiods. 



which had been exposed to five 8-hr photoperiods after Grand Rapids 

 lettuce seeds had been implanted and covered with a light-tight wrap- 

 per. Approximately 40% of the implanted seeds germinated. Figure 3 

 (lower) illustrates a petiole from a Xanthium plant which had been 

 exposed to five 20-hr photoperiods. This petiole contains no germi- 

 nated seed; in related experiments, however, in which larger samples 

 of seeds from the same lot were similarly treated, up to 5% germina- 

 tion was observed. 



The implanted petioles shown in Fig. 4 were covered with trans- 

 parent Saran Wrap rather than with light-tight aluminum foil. A direct 



Fig. 4. Germination of Grand Rapids lettuce seeds implanted under 

 transparent Saran Wrap covers in petioles of Xanthium plants maintained 

 on 8-hr (above) and 20-hr (below) photoperiods. 



