No. 544] ORIGIN OF UNIT CHARACTERS 



Since, however, the behavior of somatic characters 

 forms our only means of knowing whether the deter- 

 miners are continuous or discontinuous, it is obvious 

 that this opinion requires further examination in the con- 

 ceptions of Johannsen. 



5. Johannsen's Pure Lhir Theory™ 

 The theoretic contrast between the real discontinuity 

 of the blastic determiners and the delusive continuity 

 of visible or somatic form is pushed to its extreme in 

 the " pure-line" conception which marks the latest de- 

 velopment in heredity, an advance upon Weismann's 

 germ-plasm theory and Mendel's unit-character law. 

 Through experiments on successive generations of self- 

 fertilizing plants (the garden bean), Johannsen has 

 reached a standpoint which may be briefly stated as 

 follows : 



A "pure line" is composed of the descendants of one pure strain 



