198 CHEMICAL AGENTS AND GROWTH 



have distinct effects on the germination of Grand Rapids lettuce seed, 

 and that treatment with either of these chemicals cannot substitute 

 for red lisht treatment under selected conditions. Thus the effect of 

 any one of these three agents can be separated from the effects of the 

 other two. The results contradict the hypothesis that the photoreaction 

 controls germination of Grand Rapids lettuce seed solely by regulating 

 the levels of endogenous gibberellin- or kinin-like substances. 



MATERIALS AND METHODS 



Seeds of Lactuca sativa, var. Grand Rapids, were obtained from 

 Mayo Seed Co., Knoxville, Tennessee. They were germinated in 

 covered 9-cm petri dishes containing pads of filter paper moistened 

 with appropriate solutions at pH 5.8 and exposed to light only at the 

 times indicated. Dishes were transferred to and from rooms at different 

 temperatures in a light-tight box. Red and far-red treatment affected 

 only the rate of germination in darkness at 22 °C, since germination 

 of far-red treated seeds was complete if subsequently given sufficient 

 time in darkness. This behavior corresponds to that exhibited by the 

 Grand Rapids seed used by Evenari et al. (1953). The criterion for 

 germination at any time was the visible appearance of the radicle. 



Unless otherwise indicated, each treatment was represented by two 

 dishes, each containing approximately 120 seeds. Germination among 

 replicates was shown, by the chi-square test, to be attributable to 

 chance variations among seeds drawn at random from a single popula- 

 tion. On the basis of this test, the replicate data were pooled for 

 further analysis. Chi-square tests were then applied to the 2X2 

 contingency tables formed by considering all possible treatment pairs 

 within one experiment. Differences concluded significant were those 

 for which P < 0.001. It should be noted that within any one experi- 

 ment, the chi-square tests so applied are not independent. This formal 

 objection was overcome by the application of Tukey's method for 

 comparison of means after percentage germination in each dish had 

 been transformed by the inverse sine transformation. This procedure 

 yielded differences significant at the 5% level. A description of these 

 statistical procedures is given by Snedecor (1956). 



