136 THE QUANTITATIVE METHOD IN BIOLOGY 



With reference to the visible properties, two sorts of seeds exist 

 (see (3)) : round seeds represented by D^ + 2DR ( = T + f = f)» 

 and wrinkled seeds represented by R^ ( = t)- The ratio is 

 round : wrinkled ='^ : i. 



In MENDEL'S experiment 7324 seeds were obtained ; 

 among them 5474 were round or roundish and 1850 angular 

 wrinkled. Therefrom the (observed) ratio 2-96 to i is de- 

 duced.^ 



With reference to the hereditary possibilities, two sorts of 

 round seeds exist : a first sort represented by the term D^ 

 (numeric value J), which is able to produce round seeds only, 

 and a second sort represented by the term 2DR (value f), 

 which contains the factors D and R and may therefore produce 

 round and wrinkled seeds. Therefrom (among the plants raised 

 from round seeds) the ratio plants yielding i sort of seeds : plants 

 yielding 2 sorts of seeds = i : f = i : 2. 



In MENDEL'S experiment, among 565 plants which were 

 raised from roimd seeds 193 yielded round seeds only ; 372, 

 however, gave both round and wrinkled seeds. Therefrom the 

 (observed) ratio i : 1-93 is deduced.^ 



(5) The sum of the three coefficients (1 + 2 + 1 = 4) expresses 

 the number of sorts of possible compoimd events (sorts of 

 seeds), the order of succession of the simple events (dis- 

 tinction between $ and $ germ cells) being taken into 

 account. 



(6) The letters of each term indicate the constitution of the 

 corresponding compound event ; in other words, the hereditary 

 causes or factors contained in the corresponding sort of seeds. 

 (See (4).) 



(7) The coefficient of each term indicates in how many ways 

 the corresponding compound event may be brought about ; 

 in other words, in how many ways the corresponding seeds may 

 be produced. The seeds D^ (coefficient i) and R^ (coefficient i) 

 are produced each in one way {D $ x D ^ ; R $ x R ^). 

 The seeds 2DR are produced in two ways [D f x R ? or 

 D i xR $). 



Each coefficient indicates, moreover, how many sorts of 

 seeds (Fg generation) may be yielded by the corresponding 

 plants. (See (4).) The plants raised from the seeds D^ will 

 produce one sort of germ cells (Z)) and therefore one sort 

 of seeds (just as the parent S). For the same reason the 

 plants raised from the seeds R^ will yield one sort of seeds 

 (as the parent />). The plants raised from the seeds 2DR will 

 produce two sorts of germ cells and (with regard to the visible 

 properties) two sorts of seeds, as the plants {DR) of the Fj 

 generation — viz. 

 1 See MENDEL, in BATESON, loc cit., p. 326. ^ 11,1^., p. 329. 



