THE STUDY OF NATURAL SELECTION 



i35 



In these experiments the seeds were all carefully examined to make 

 sure that they were perfectly developed 24 and differed only in size. 25 

 The biometric constants of 28 series which developed into mature 

 plants have been compared with those for the original series of seeds 

 from which the plantings were drawn. 26 



Diagram 2. Differences in Mean Weight of General Population of Seeds 

 and of those which Producb Plants. All differences are reduced to a percentage 

 basis. 



The results of these studies can be most conveniently presented 

 graphically. To demonstrate more clearly to the eye the existence of a 



done on too small a scale to be conclusive. Possibly among these writings some 

 records of the viability of seeds of different sizes may be found. 



23 J. Arthur Harris, ' ' On Differential Mortality with Respect to Seed Weight 

 Occurring in Field Cultures of Phaseolus vulgaris," Amer. Nat., 46: 212-225, 

 1912. 



21 Unfortunately many students of seed weight in its relation to viability or 

 productiveness have not distinguished between small but perfectly developed 

 seeds and those which are blighted or shriveled and immature. It is not at all 

 unlikely that very different results will be secured from the two sorts. 



25 Weighings were made of each seed in units of .025 grams, that is, 0.000- 

 0.025 grams = 1 unit, 0.025-0.050 = 2 units, etc. 



28 Since the seeds were taken quite at random any stringent selective mor- 

 tality will be seen in the differences between the constants of the original bulk 

 of seeds weighed and those of the sub-samples planted which actually developed 

 to maturity. The method might not be adequate for a very low selective death 

 rate. In any case it must be expected to give irregular results. A much more 

 satisfactory method is to draw the comparisons between the constants of the 

 seeds which died and the constants of those which developed. Appropriate data 

 for field culture series are being collected. Large greenhouse cultures in sand 

 in which the comparisons can be made between the seeds actually developing and 

 those failing to develop fully substantiate the conclusions drawn from field tests. 



