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 lumping of the two sets of experiments which differ in some slight but apparently 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.[1]
Diagram 2 shows the relative differences in type (mean seed weight)[2] between the total samples of seeds weighed and those which produced plants.[3]
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 seeds 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 relationship 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
- ↑ J. Arthur Harris, "Supplementary Studies of the Differential Mortality with Respect to Seed Weight in the Germination of Garden Beans." To be published shortly.
- ↑ 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 multiplying the difference by 100 and dividing by the mean for the general population.
- ↑ 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.
