MEASUREMENT OF VARIABLE PROPERTIES 141 



In MENDEL'S experiment the figures were : 



Observed 



(v) Plants bearing Dr seeds . 



{&) „ Dr and Rr seeds 



35 



67 



Calculated 



102x^ = 34 

 102 x-|=68 



The plants raised from wrinkled green seeds — that is to say, 

 from (') i?V2 — were expected to bear one sort of seeds (wrinkled, 

 green). 



In MENDEL'S experiment 30 fertile plants raised from 32 

 seeds yielded seeds Rr.^ 



§ 106.— ELEVENTH EXAMPLE (continued) .—In a third 

 experiment MENDEL crossed two varieties (subspecies) of the 

 edible pea differing in three primordia — viz. 



Parent « Parent /S 



Seed round (A) Seed wrinkled (a) 



Albumen yellow (B) Albumen green (6) 



Seed-coat grey-brown (C) Seed-coat white (c) 



The seeds (first hybrid generation Fj) are ABC as the parent 

 a, the primordia A, B, C being dominant. 



The plants raised from these seeds yielded (by self-fertiliza- 

 tion) numerous sorts of seeds. In order to calculate all the 

 possible compound events (sorts of seeds), the method indicated 

 for the second experiment (p. 138) may be followed — viz. 



For the three pairs of primordia all the possible combinations 

 of the germ cells are obtained by working out — 



(A + a)^x(B + b)^x{C+cY 



1 The plants raised from seeds Rr yield in their turn seeds Rr and so on in all 

 the subsequent generations. All these plants are similar to the parent 6. In 

 many crosses between two species a and 6 differing in two pairs of properties, 

 the recessive property R belongs to a and r belongs to b. In all such cases the 

 plants Rr are characterized by a NEW combination of two properties which 

 do not coexist in any of the parental species. Since the new combination Rr 

 is transmitted without any variation to all the successive generations it may 

 be said that a new specific form (constant hybrid) has been produced. A 

 si mila r remark is applicable to the combination abc in § io6 and to any com- 

 bination of recessive properties. 



It may be recalled that a new specific form may be produced in four different 

 ways — viz. 



(i) By a saltation (mutation) which is a direct result of a change in the con- 

 ditions of life (§§ 8a and g). 



(2) By a saltation which is an indirect result of a change in the conditions of 



life (§ 9). 



(3) By a cross between two specific forms, the new form being interposed 

 between the parental species § 35). 



(4) By a cross between two specific forms, the new form being characterized 

 by a new combination of properties. 



