366 



The Journal of Heredity 



up anyhow. The right-hand pack rep- 

 resents the female gametes, and the 

 left-hand pack the male gametes. 



Now take up one card from the top 

 of each pack, as shown in Fig. 13. 



Fk;. 13 



There arc four possible pairs which 

 vou can jjick up in this wav : Red Black, 

 Red Red, Black Red and Black Black. 

 Make four columns on the blackboard 

 or a sheet of paper, with these headings, 

 and put down a unit for every combina- 

 tion as it is taken up from the packs. 

 If the cards have been thoroughly 

 shuffled there will be thirteen units 

 under each heading. If the cards have 

 not been thoroughly shuffled, there may 

 be a deviation: instead of 13, 13, 13, 13, 

 we may get 12, 14, 14, 12, or something 

 similar. If this occurs, shuffle the same 

 packs and try again. I have always 

 found that the ratio comes out correctly 

 the second time. 



Taking ujj the analogy again, we have 

 the comlnnation Black Black re]:)re- 



senting the pure dominants. Their 

 germ-plasm has thrown out the red 

 altogether and contains nothing but 

 black; as long as they are self-fertilized, 

 they will breed pure black generation 

 after generation. 



The next two combinations are Black 

 Red and Red Black; but as black is 

 dominant, it is evident that these will 

 look and behave just alike, the black 

 in each case concealing the red, which 

 remains recessive or latent. These 

 combinations are known to the Mende- 

 list as hctcrozygotes, or impure domi- 

 nants, while the pure black or pure red 

 is called a homozygote. 



Finally, the combination Red Red 

 represents the pure (or "extracted," 

 as it is often called) recessive. This 

 line of germ-plasm has gotten rid of all 

 the black, and will breed pure red 

 indefinitely, provided it be self-fertilized 

 and no new dominant introduced. 



As to the hctcrozygotes, the Black Red 

 and Red Black combination, it will be 

 evident to the reader, if he thinks back 

 over the whole process, that when they 

 are again self-fertilized, they will again 

 split up into the simple IMendclian 

 proportion of three dominants (two of 

 which are impure) to one recessive. 

 And so the process goes on, generation 

 after generation, where a single pair of 

 contrasted characters (called "allelo- 

 morphs") is concerned, each generation 

 seeing a segregation of the characters 

 according to the law of chance, just as 

 if the characters were shuffled about by 

 Nature as we shuffle the cards; and 

 each generation seeing a rcj^etition of 

 the famous 3:1 ratio. 



Improving Native Grapes 



Like several other southern States, Georgia is endeavoring to exploit the hardy 

 native grape (Vitis rotundifolia), either through selection or h\'bndizalion. So far 

 the work accomi)lishcd at the State Exiicriment Station has been preliminary, 

 and devoted to a study of the behavior of the white scuppcrnong variety under 

 carefully controlled conditions, so that its characters could be determined. The 

 pecan, which has attained considerable importance in the South during recent 

 years, is also under investigation, to determine why a number of trees are self- 

 sterile, and what advantage lies in keeping such trees in an orchard. 



