APPENDIX II 301 



This is Mendel's Law of Inheritance of unit-characters. 

 It reveals : 



1. That when unit-characters only are selected a 

 hybrid is always like one or other of the parents. 



2. That we can only ascertain that such a cross is a 

 hybrid by sowing its seeds, when the latent quality will 

 reappear among the individuals of the next generation. 



3. That when sufficient individuals are taken, a certain 

 mathematical ratio is found to exist between the Hybrids, 

 pure Dominants and Recessives of any of the succeeding 

 generations. 



Now this ratio, experimentally obtained and confirmed 

 again and again, admits of a very simple interpretation. 

 In the process of sexual reproduction the total number 

 of possible gametic fusions, male ( c? ) and female ( ? ), 

 which can be obtained by crossing a Dominant form D 

 with a Recessive form R is obviously the number of com- 

 binations which can be formed by associating together 

 the following couples: 



<? D X ? D =1 pure D. 

 fS Wr} = 2 impure D's. 

 ? R X c? R =1 pure R. 



Thus the Mendelian Law has a physiological basis, the 

 constitution of the hybrid being explained by the prin- 

 ciple of what is known as the Segregation of the Gametes 

 in the generations that foUow. 



When two or more unit characters are combined the 

 resulting ratios are more complicated, but several of these 

 have been worked out mathematically and demonstrated 

 practically. 



An enormous amount of work has been accomplished 

 during recent years on the transmission of aU kinds of 

 unit-characters in plants and animals, and in spite of much 

 slipshod and misleading work which has been published 

 as bearing upon Mendelian inheritance, many reliable 

 results have been obtained, some of which have tm-ned 

 out to be of great economic value. No modern horticul- 

 turist or animal-breeder can now afford to be ignorant 

 of this important discovery in the realm of heredity. 

 It is even important in investigating the transmission of 

 many human characters. 



