TEE STUDY OF NATURAL SELECTION 145 



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. 62 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 53 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 asymmet- 

 rical — are less capable of maturing their ovules into seeds than are 

 those with an " even " number. Again, 54 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 develop- 

 ment, in Phaseolus shows (by two different tests) a physiological ineffi- 

 ciency. 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. 



H The soundness of the conclusions of the papers there reviewed has been 

 emphasized by a research which has appeared since that time ("Further Ob- 

 servations on the Selective Elimination of Organs in Staphylea," in Zeitschr. 

 f. Ind. Abst.- u. Vererbungsl., 5: 273-288, 1911). Here it is rendered highly 

 probable that the observed selective mortality of ovaries can not be explained by 

 such simple factors as a correlation between the position of the ovary on the 

 inflorescence, with a heavier but purely random mortality in certain regions of 

 the inflorescence. In another paper on methods ("On the Formation of Con- 

 densed Tables when the Number of Possible Combinations is Large," Amer. 

 Nat., 46: 477-486, 1912) evidence is brought forward for an interesting morpho- 

 genetic relationship between radial asymmetry of the compound ovary and its 

 locular composition. 



88 J. Arthur Harris, ' ' On the Eelationship between Bilateral Asymmetry and 

 Fertility and Fecundity," Boux's Archiv. f. Entwichelungsmechanik, 35: 500- 

 522, 1912. 



M J. Arthur Harris, ' ' On the Eelationship between the Bilateral Asymmetry 

 of the Unilocular Fruit and the Weight of the Seed which it Produces, ' ' Science, 

 N. S., 36: 414-415, 1912. 



