No. 531] GENOTYPE CONCEPTION OF HEREDITY 135 



which the individuals fluctuate. For the descriptive- 

 morphological view the manifestations of the phenotypes 

 in different generations are the main point, and here the 

 transmission-conception immediately announces itself. 

 Hence we may adequately define this conception as a 

 "phenotype-conception" in opposition to the genotype- 

 conception. 



As already stated, the genotype-conception has been 

 gained in two ways: pure line breeding and hybridization. 

 The first way leads to an analysis of the existing stocks 

 or populations, the second way may realize an analysis of 

 the genotypical constitution of the individuals. The 

 analysis of populations has its most obvious importance in 

 all such cases, where the phenotypes are quantitatively 

 characterized. Even where individuals with consider- 

 able genotypical differences co-exist, the population may 

 —by simple inspection or by statistical appreciation— seem 

 to exhibit only one phenotype, this being usually charac- 

 terized by the average measure of the individuals (dimen- 

 sions, weight, intensity of any quality, number of organs 

 and so on). This is due to the fluctuating variability 

 swamping all limits between the different special pheno- 

 types in question (see the diagram). 



Populations of self -fertilizing organisms (several 

 cereals and beans, peas and others) have offered the 

 starting point for pure line breeding as a scientific 

 method of research. A pure line may be defined as the 

 descendants from one single homozygotic organism, ex- 

 clusively propagating by self-fertilization. "Pure line" 

 is a merely genealogical term, indicating nothing as to 

 the qualities of the individuals in question. A "line" 

 ceases to be "pure" when hybridization (or even inter- 

 crossing) disturbs the continuity of self-fertilization. 



From a population of homozygotic self-fertilizers 

 there can be started (isolated) as many pure lines as 

 there are fertile individuals— of course very many of 

 such pure lines will be quite identical in genotypical 

 constitution and might in reality belong to one and the 



