CORRELATION OF Xanthium AND LETTUCE SEED 305 



Table I. Germination of Grand Rapids Lettuce Seeds 

 Implanted in Petioles of Xanthium Plants 



Germination of Lettuce Seed, % 



° Implanted petioles covered with Saran Wrap. 



* Implanted petioles covered with aluminum foil. 



"^ Eighty percent germination in vitro in darkness at 20°C in 48 hr. 



^ Two percent germination in vitro in darkness at 20°C in 48 hr. 



ity of some inhibition of germination even when the Xanthium hosts 

 are exposed to 8 hr of Hght daily. 



Direct illumination of seeds implanted in petioles of Xanthium 

 plants on 8-hr photoperiods results in an increase in the percentage of 

 seeds which oerminate. On the other hand, as seen in Fies. 3 and 4 and 

 Table I, illumination of the seeds appears to have little or no effect on 

 germination when the cocklebur plants are under 20-hr photoperiods; 

 inhibition is not reversed by illumination of implanted seeds. 



The source of the inhibitory influence appears to be in the leaf 

 blades. If the leaf blades are removed after the petioles have been im- 

 planted and wrapped with aluminum foil, the germination of the im- 

 planted seed is unaffected by the subsequent photoperiodic treatment 

 of the Xanthium host. 



In the second approach to the stimulation vs. inhibition problem, 

 seeds of White Paris Self Folding Cos, a nonphotosensitive variety of 

 lettuce, were used in implantation experiments. Table II shows ger- 



Table II. Germination of Seeds of White Paris Self Folding 

 Lettuce (Dark) Implanted in Xanthium Petioles 



Germination of Seed," % 



Photoperiod, hr 



{Xanthium) Expt. 1 Expt. 2 



8 86.5 61.7 



20 37.8 8.0 



" Implanted [jelioles covered with aluminum foil. 



