134 THE QUANTITATIVE METHOD IN BIOLOGY 



reactions, acid, alkaline, neutral, have been calculated a priori. 

 In TableJA they are compared with the observed frequencies 

 (deduced from Table t) : 



§ 104.— ELEVENTH EXAMPLE: APPLICATION OF 

 THE PRINCIPLES OF PROBABILITY (FREQUENCY) 

 TO THE HEREDITARY TRANSMISSION OF PRIMORDIA 

 IN MENDELIAN HYBRIDS.— In § 33 (p. 32) I have given a 

 short account of MENDEL'S experiments and principles. Let 

 us now consider this subject from the standpoint of the rules 

 of chance. 



In one of his classic experiments with the edible pea 

 MENDEL crossed a variety (subspecies) S with round seeds 

 (primordium D) with a variety p with wrinkled seeds (pri- 

 mordium R). In this cross each egg or seed (hybrid of the Fj 

 generation) is made by the union of a germ cell D taken from 

 the parent S and containing a certain cause or factor corre- 

 sponding to the primordium D, and a germ cell R taken from p 

 and containing a factor corresponding to the property R. Both 

 germ cells are, of course, taken at random ; their union is a 

 compound event. One possibility exists (compare § 91) : the 

 production of an egg or seed DR in which the causes D and R 

 meet each other.^ The coexistence of both factors brings about 

 a reaction by which the dominant primordium (state of equi- 

 librium) D becomes visible, whereas R is concealed or latent 

 (compare Example (D), p. 130) : all the seeds are round. 



From the seeds DR (F ^ generation) plants F^are raised which 

 give birth to $ and $ germ cells. According to the principle 

 of segregation, the germ cells are of two sorts, D and R, both 

 sorts being in equal number among the $ just as among the $ . 

 The plants are fertilized with their own pollen, the $ and the ? 

 germ ceUs being united according to the rules of chance. If we 

 suppose that, for instance, the ^ germ cells are 500 D + 500 R 



1 It is supposed that the i and the 9 germ cells are equivalent with regard 

 to the hereditary transmission of the primordia. 



