ULTRA-VIOLET AND SEED PLANTS 857 



tion, fluctuations are so great that it would hardly be justifiable to 

 attribute this to a stimulating effect of the region between 3000 and 

 4000 A. 



Mezzadroli and Vareton (61, 62), Popoff (68), and Malhotra (50) also 

 claim to have obtained favorable effects on germination and early 

 seedling growth by means of ultra-violet radiation. In all cases the 

 conclusions do not seem justifiable from the experimental data presented. 

 For a more detailed criticism of their work the reader is referred to Popp 

 and Brown (74, pages 167-168). 



One of the most recent papers in which stimulation of early develop- 

 ment of seeds is claimed is that of Masure (55). He has watched the 

 behavior for 4 days of pea seeds kept in the dark after irradiation for 

 various lengths of time with a mercury-vapor arc in quartz through a 

 Corning G586AW screen. The range of this filter was given as 3334 to 

 3690 A with a maximum transmission in the region 3650 A. 



In the summary of the paper only the possible demonstration of 

 stimulation is mentioned, although earlier in the paper the author gives 

 data which he himself states as indicating lack of stimulation. For 

 instance, under no conditions of exposure in which the rate of germination 

 was recorded did the irradiation of dry or soaked seeds influence in any 

 significant degree the rate of germination. As stated by the author, 

 "The results obtained allow only one conclusion to be draw^n, namely, that 

 raying has no marked effect on the rate of germination." Moreover, 

 the data including average hypocotyl lengths of seedlings subjected to 

 statistical analyses "do not indicate that the raying had a distinctly 

 significant effect on the seeds." 



The author's statistically significant figures indicating stimulation 

 were obtained by comparing frequency distributions of root growth of 

 seedlings of related pairs of lots of rayed and control populations. In this 

 comparison the frequency-distribution curves for a treated and a corre- 

 sponding control lot were plotted on the same sheet of graph paper, and a 

 comparison made of the shift of the treated relative to the control popula- 

 tion. By thus abandoning "average growth values" as masking the 

 effect of raying and resorting to statistically analyzed frequency-distribu- 

 tion curves of root growth, he has obtained significant figures in favor of 

 raying; that is, the percentage number of seedlings of rayed lots growing 

 as fast as the fastest third of control lots was greater for rayed groups. 

 While the statistical methods used seem to be satisfactory, the author has 

 failed to give the data which would enable one to determine actual 

 population distributions, upon which his only demonstration of stimula- 

 tion is dependent. Furthermore, it cannot be overemphasized that w'hile 

 statistical analyses may show significant differences between test plants 

 and controls, no statistical method in any sense indicates that one of a 

 multiple of operating factors is the sole cause of the significant difference 

 unless all of these factors are taken into account. 



