118 CARNEGIE INSTITUTION OF WASHINGTON. 



PURE LINES. 



Influence of Weight of Seed upon the Character of Plants Produced, 

 by J. A. Harris. 



The question of the relationship between the weight of the seed 

 planted and the characteristics of the plant produced — a problem 

 which has necessarily been taken up at this Station because of its 

 bearing upon questions of pure-line inheritance — -is one of consider- 

 able practical importance. Extensive studies have shown that in 

 Phaseolus there is regularly a positive correlation between weight 

 of seed planted and number of pods per plant — yield increasing with 

 weight of seed planted. But the correlation for weight and char- 

 acter of pods, that is, number of ovules formed and number of seeds 

 matured, is much lower and is reduced practically to zero when cor- 

 rection for number of pods is made. Thus the yield in number 

 of pods but apparently not the character of the pods produced is 

 directly influenced by weight of seed planted. 



Selection within the Pure Line, by J. A. Harris. 



The studies on pure-line inheritance for seed weight have been 

 continued, but publication has been delayed because of the many 

 difficulties of analysis introduced by various physiological correla- 

 tions. The number and magnitude of these difficulties has never 

 been fully enough taken into account by those who have written on 

 these questions. For example, the work at this Station has shown 

 that there is a sensible correlation between the weight of the seed 

 and the number of pods produced by the plant. There is also a 

 correlation between the number of pods on the plant and the weight 

 of the seeds which it produces. As a resultant of these correlations 

 some relationship must be expected between the weight of the parent 

 and offspring seed in the population. Again, our experiments on 

 differential mortality with respect to seed weight show that physio- 

 logically considered this character is by no means a simple one. To 

 distinguish relationships between parental and offspring seeds which 

 are purely physiological from those which are genetic is a problem 

 requiring further experimentation. 



Selection for seedling abnormahties was begun in 1912 and carried 

 out on a larger scale this year. It is too early to report results, 

 although it may be noted in passing that some abnormal parents 

 threw all abnormal offspring this year. 



CLONAL. 

 Heredity in Parthenogenetic and Clonal Reproduction. 



AMiile the term "pure line" is strictly applicable only to self- 

 fertilizing species, it is reasonable to expect that parthenogenetic 

 and non-sexually reproducing species shall follow the same laws of 

 heredity; and several studies have been made here with such species. 



