Page:Popular Science Monthly Volume 84.djvu/149

Rh ovules into seeds, or in the formation of well-developed seeds—may be found.

Obviously, it will be of great advantage if direct demonstrations of the action of natural selection can be supplemented (or in some cases it may be preceded) by evidences of an entirely different sort.

Such supplementary evidences have so far been sought only in the case of the organization of the plant ovary. Studies of the selective elimination of ovaries have been reviewed in the earlier paper on the measurement of natural selection. Since then considerable side light has been thrown upon the problem of the intra-individual selective elimination of organs by two studies of a purely physiological character.

One of the characters dealt with in studies of the development of the ovary is the "odd" or "even" number of ovules which it produces. This is essentially a criterion of the bilateral asymmetry of the plate of carpellary tissue giving rise to a locule. In large series of pods of garden beans it has been shown that pods with an "odd" number of ovules—that is, those which have the ovules unequally divided between the two carpellary margins, and are consequently bilaterally asymmetrical—are less capable of maturing their ovules into seeds than are those with an "even" number. Again, all the available data indicate that the weight of the seeds is lower in pods with an "odd" than in those with an "even" number of ovules.

The interest of these results is heightened by the fact that the type of structure which in Staphylea shows an inferior capacity for development, in Phaseolus shows (by two different tests) a physiological inefficiency. As soon as proper materials and technique are available it will be of importance to consider asymmetry in its relation to the capacity for survival of the individual.