136 TEE POPULAR SCIENCE MONTHLY 



differential mortality with respect to seed weight, I have combined in 

 Diagrams 2-3 the data from the field trials already published with 

 those from a series of experiments on germination in sand. The lump- 

 ing of the two sets of experiments which differ in some slight but ap- 

 parently significant details to give sufficient series to make smooth 

 graphs is justified by the fact that individually they lead to essentially 

 the same conclusions and that the data and minute comparisons are to 

 be presented in full detail eventually. 27 



Diagram 2 shows the relative differences in type (mean seed 

 weight) 28 between the total samples of seeds weighed and those which 

 produced plants. 29 



Here the heavy vertical bar represents zero difference between the 

 average weight of the total population of seeds and those which actually 

 produce plants. The broken lines and circles to the right show on the 

 scale at the bottom, where each unit represents one tenth per cent, the 

 number and amount of the positive differences, that is to say of those 

 in which the seeds which survived are heavier. The heavy lines and 

 solid dots to the left of the zero bar indicate the number of experiments 

 giving negative differences — i. e., in which the mean weight of the 

 series of seeds which produced plants was less than that of the general 

 population — and the amount of the difference in relative weight. 



Judging the areas of light and dark shading, by the eye alone, one 

 would conclude that the surviving 6eeds are slightly heavier than the 

 population from which they were drawn. But the deviation from the 

 equality of division which would be expected if there were no relation- 

 ship between the weight of the seed and its capacity for survival is only 

 4 ± 2.98 cases, and little significance can be attached to it. For the 



2T J. Arthur Harris, ' ' Supplementary Studies of the Differential Mortality 

 with Eespect to Seed Weight in the Germination of Garden Beans. " To be pub- 

 lished shortly. 



28 Several varieties of beans grown under diverse cultural conditions are 

 involved. The varieties with the largest seeds are about three times as heavy as 

 the smallest. To express the differences in absolute weights has its advantages, 

 but when the number of series involved is too large for individual labeling in 

 the graph, it is best to reduce values to a relative (percentage) basis by multi- 

 plying the difference by 100 and dividing by the mean for the general population. 



28 Here lies one of the objections to combining the two series of experiments. 

 In the field culture the eliminated seeds were those which failed to produce fertile 

 plants. In the sand cultures the fate of a seed could be followed only to 

 germination. Some of the seedlings were abnormal, but to avoid all possibility 

 of criticism every seed which germinated at all was included in the viable class. 

 Doubtless in field cultures some of these would have perished before producing 

 seeds. By retaining all these we are possibly making out a poorer case for 

 differential mortality than we might by considering a part of the abnormal 

 seedlings incapable of survival to maturity under field conditions. 



