PEDIGRKE-CULTURE. 23 



To attain to perfect knowledge of ancestry, the ideal 

 toward which the pedigree-culturist strives, many precau- 

 tions are necessary, and as the fundamental character of the 

 problems of genetics is bound to attract increasing numbers 

 of investigators, it is thought that the writer's experience in 

 the conduct of experiments involving the pedigree-breeding 

 of plants at the Station for Experimental Evolution may be 

 of use to others who have occasion to take up such work, and 

 this is the author's motive in presenting the following account 

 of methods used. 



Perfect knowledge is a high ideal and not absolutely 

 attainable, because some sources of error can not be elimi- 

 nated. This is due principally to the fact that they are of the 

 nature of catastrophes which can not be foreseen; hut if 

 reasonable care is taken the results will usually be so decisive 

 as to leave no doubt of their correctness, and in cases of 

 doubt, where it may be assumed that some unexpected and 

 unknown error has crept in, the cultures may be and should 

 be repeated. The same accident is not likely to occur a sec- 

 ond time to the same pedigree. A pedigree with a question- 

 mark in it is usually no better and often very much worse 

 than no pedigree, and any material whose pedigree is in 

 doubt should be at once eliminated, or if the material is 

 rare and valuable in itself, it should be treated as any other 

 unknown material, namely, assigned a distinct pedigree-num- 

 ber or other designation which gives no suggestion of rela- 

 tionship to other known material. Cultures grown from such 

 questionable material may indicate its relationship by the 

 characters presented, but knowledge of this relationship 

 rests purely on inference, and that inference is just as trust- 

 worthy in itself when no hint of probable derivation has 

 been noted as when the record indicates a probable but 

 doubtful origin. 



The most important factor in the elimination of errors 

 is a high ideal in this regard on the part of all those who 

 have anything to do with the cultures. Mind and senses 



