VAEIATIOX IX PEDIGEEE-CULTUEES 



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others may be arranged in a continuous series which shades by the 

 smallest increments from one to the other. In making such an ar- 

 rangement, it will be found that the greater number resemble, or lie 

 near, an individual or group of individuals at some place along the 

 line between the two extremes. Statistical measurements of this or 

 any other quality may be made, and the position of the norm of the 

 type determined accurately, as well as the range of variability. In like 

 manner, the correlation between any two characters or qualities may be 

 worked out. Xow, having in hand such a mass of data from the initial 

 culture, a fair basis is had for taking up various questions. Thus 

 a succeeding generation might be grown in soil deficient of any nutri- 

 tive factor, or poor in all of them, in rich soil, or in a substratum 

 highly charged with any element, or at unusual temperatures for the 

 purpose of determining the extent and manner in which the range of 

 variability may be altered by such special treatment, and this may be 

 accentuated by the continuance of the test in successive progenies. 



Then again the pedigree-culture offers a fair opportunity for a 

 demonstration of the influence of the effects of selection upon the range 

 of variability and the mean value of any quality. Comparative cultures 

 of seeds taken from the widest-leaved individuals with those of the 

 narrower leaves will tend to show the result of such selection, especially 

 if the selection is continued through several generations. In all these 

 tests it is assumed that the seeds for the following generations should 

 in all instances be guarded as directed above and sown in sterilized soil. 

 With such close series of cultures the question of self- and close-fertil- 

 ization might arise, and here again the culture affords invaluably exact 

 material for a test of a subject upon which but little definite informa- 

 tion exists. 



Fig. 2. Seed-pans and Plantlets of CraUegus, in Puke Cultures, Arnold Arboretum 



