ON DIFFEBENTIAL MOETALITY WITH RESPECT 

 TO SEED WEIGHT OCCURRING IN FIELD 

 CULTURES OF PISUM SATIVUM 



DR. J. ARTHUR HARRIS 

 Carnegie Institution of "Washington 



In two papers which have already appeared in these 

 pages, 1 I have shown that for the dwarf varieties of 

 Phaseolus vulgaris the mortality of apparently perfect 

 seeds (failure to germinate or to complete the life cycle) 

 is not random, but differential, or selective. 



It seemed highly desirable to extend these studies to 

 other forms. Pisum sativum naturally occurred to me as 

 affording suitable experimental material — both because 

 of the wide range of seed characteristics and the conve- 

 nience with which it may be bred. I had no pedigreed seed 

 and consequently began work in the spring of 1913 with 

 commercial stock. About 1,000 seeds from each of ten 

 early (dwarf) varieties purchased from the Thorburn 

 seed company were weighed, individually labelled and 

 planted in short rows scattered over one of the fields of 

 the Station for Experimental Evolution. Conditions 

 were not the best, and the mortality was high. 



Table I 2 gives the weights in units of .025 gram range 3 



1 Harrk, J. Arthur, "On Differential Mortality with Eespect to Seed 

 Weight Occurring in Field Cultures of Phaseolus vulgaris," Ameb. Nat., 

 46: 512-525, 1912; "Supplementary Studies on the Differential Mortality 

 With Respect to Seed Weight in the Germination of Garden Beans," Ameb. 



2 For convenience the series may be designated by letters: A, Witham 

 Wonder; B, American Wonder; C, Premium Gem; D, Little Gem; E, Nott's 

 Excelsior; F, Sutton's Excelsior; G, Laxtonian; E, Little Marvel; /, Peter 

 p an ; J, English Wonder. 



J Class 1 = 0.000-.025 gram, . . . class 4 = .075-.100, class 5 = .100- 

 •125, and so on. Thus to obtain means or standard deviations of weights in 

 grams, deduct .5 from the values in the tables and multiply by .025. 



