536 THE POPULAR SCIENCE MONTHLY 



mean number of ovules is materially increased. For a small series of 

 developing ovaries taken at the Missouri Botanical Garden in 1906, the 

 oldest — the group from which the most elimination had taken place — 

 had about eight per cent, more ovules per fruit than the youngest. In 

 large samples taken in 1908, the fruits which matured had about seven 

 per cent, more ovules than those which were eliminated. The same re- 

 sult is seen if the material is split up into twenty-eight individual 

 pairs of samples, each from a separate tree. This is made clear by Fig. 

 5. The solid dots connected by broken lines show the percentage excess 

 of the matured fruits over the fallen ovaries in the number of ovules. 

 In twenty-seven cases out of twenty-eight the number is larger in the 

 ovaries which mature ! 



Youngest. Oldest. 



Fig. 6. Pbbcentage of Ovaries which abb pebfectlt badially Symmetbical in 

 YOUNGEST AND OLDEST COLLECTIONS, Mlssourl Botanical Garden, 1906. 



The ovary of Staphylea is three-celled. If each cell contains the 

 same number of ovules, e. g., 8-8-8, it may be regarded as radially 

 symmetrical, while if the numbers differ from locule to locule, for in- 

 stance 8-7-8 or 9-10-8, the ovary may be described as radially asym- 

 metrical. If this radial asymmetry be expressed by a statistical con- 

 stant such that a perfectly symmetrical fruit shall have a degree of 

 asymmetry of 0, while the coefficient increases as the ovaries become 

 more irregular, one can compare asymmetries in the ovaries which do 

 and those which do not develop to maturity as easily as he can the 

 means. 



Fig. 6 shows the percentage of perfectly symmetrical" ovaries in the 

 youngest and oldest series of the 1906 collection. The conclusion that 

 the conspicuously higher percentage of perfectly symmetrical ovaries 

 in the oldest collection is due to a selective mortality by which the more 

 irregular ones are weeded out is fully substantiated by the statistics of 

 1908. 



The average asymmetry for the matured fruits for 1908 is about 

 seventeen per cent, lower than the mean for the eliminated sample. 

 For the individual trees the results are somewhat more irregular than 

 they were for the mean number of ovules, but Fig. 5 shows that in 



