No. 549] ON DIFFERENTIAL MOUT. MATY 



513 



The purpose of this paper is to present the first results 

 of a series of studies on the relationship between the 

 structural characteristics of the parent plant or of the 

 seed itself and its viability. The data here recorded 

 relate only to seed weight and are drawn from an exten- 

 sive series of field plantings of carefully selected and 

 individually weighed seeds of the common bean, 

 Phaseolus vulgaris. They are properly described as a 

 by-product, for the experiments were not carried out 

 especially nor in the most satisfactory manner to test the 

 existence of a selective mortality. 



The conditions in field cultures of individually labelled 

 seeds are such that many factors besides the weight of 

 the seed are concerned in determining whether or not a 

 seed shall develop into a mature plant. Some are lost by 

 dashing rains separating seed- and labels, after which all 

 questionable cases have to be thrown away. Some are 

 destroyed by rodents and some by the unavoidable acci- 

 dents of cultivation. In natural selection terminology, 

 the non-selective death rate — the death rate which is no 

 function of the characteristics of the individual — is very 

 high. This tends to obscure the sejective death rate, if 

 such exists. 



For just these reasons. I have never taken accc 

 the characteristics of the seeds which failed to d 



into mature plants, although the desirability of testing 

 for the existence of a selective mortality for seed weight 

 has been in mind almost from the beginning of the breed- 

 ing experiments with garden beans in 1!H)7. r | lie records 

 of those which developed to maturity were available tor 

 studies of heredity, influence of size of seed planted on 

 characteristics of the plants produced, and so on. Data 

 for the entire parental population from which the seeds 

 planted were drawn were at hand for the study of the 

 iiitlui'iices of season and environment. I nder these cir- 

 cumstances, the only need for a record of the seeds which 

 failed to develop to maturity would be for testing the 

 hypothesis of the existence of a selective death rate. As 



