QUANTITATIVE METHOD AND PRIMORDIA 41 



less {yellow and white endosperm in maize. See BATESON, 

 loc. cit., p. 41). 



In other cases a colour Z, which seems to be a primordium of 

 a species s, depends on the coexistence of two colouring sub- 

 stances a and b. When the coloured species s is crossed with a 

 colourless one, since each colouring substance is submitted to 

 segregation independently from the other (see § 33, p. 35), the two 

 components a and b (both dominant when they meet white) are 

 separated among the Fg plants according to the following 

 scheme : — 



Coloured species x Colourless species 

 (Colour Z=a + b) \ [Colour white) 



Fi 

 [colour Z) 



^ F^ 



a white 



b white b white 



[colour Z) [colour a) [colour b) [colour white) 



In this way two primordia a and b which existed but were 

 not discernible ^ in one of the parental species become visible 

 in two groups of the Fg generation. It seems as if two new 

 properties had been produced by hybridization. 



§ 37.— MENDELISM [continued). OBSERVABLE PRO- 

 PERTIES AND HEREDITARY FACTORS.— In this book 

 a property is looked upon as being a something which exists in 

 itself. I content myself with the general notion that a pro- 

 perty is the product of a reaction of the living mixture, the 

 observable symptom of a certain possibiUty, without more. 

 The scholars of the MendeUan School go further : they try to 

 analyse the possibiUties. 



They start from the hypothesis that in each species certain 

 hereditary factors (determiners) exist which bring about 

 certain reactions by which the properties are produced. In the 

 successive generations Fj, Fg . . . produced by a hybridization, 

 the factors of the parental species are brought together or 

 separated from one another according to the rule of segregation. 

 In other words, the principle of segregation is no longer appUed 

 to the observable properties, but to hypothetical hereditary 

 factors. 



The MendeUans accept further the view that certain pro- 

 perties depend on the presence of one factor, while others are 



' Certain persons who are endowed with a highly developed colour-sense 

 may be able to discern the colours a and b in the mixture Z of the coloured 

 species s (for instance, in certain subspecies of Matthiola). 



