PLANT HYBRIDIZATION BEFORE MENDEL 



309 



CLASS II 



Group 9 round yellow grey (white) 



Group 10 round green grey (white) 



Group 11 wrinkled yellow grey (white) 



Group 12 wrinkled green grey (white) 



Group 13 round yellow (green) grey 



Group 14 round yellow (green) white 



Group 15 wrinkled yellow (green) grey 



Group 16 wrinkled yellow (green) white 



Group 17 round (wrinkled) yellow grey 



Group 18 round (wrinkled) yellow white 



Group 19 round (wrinkled) green grey 



Group 20 round (wrinkled) green white 



CLASS III 



Hybrid 



Group 21 round yellow (green) grey (white) 



Group 22 wrinkled yellow (green) grey (white) 



Group 23 round (wrinkled) yellow grey (white) 



Group 24 round (wrinkled) green grey (white) 



Group 25 round (wrinkled) yellow (green) grey 



Group 26 round (wrinkled) yellow (green) white 



CLASS IV 



Hybrid 



Group 27 round (wrinkled) yellow (green) grey (white) Hybrid 



We have thus an expression with 27 terms or character-combina- 

 tions, the members of which manifestly fall into four classes. 



Class I, of 8 terms, contains plants that are constant in all their 

 characters, as can be seen by inspection, since they all contain the 

 pure dominant or pure recessive of one character, united with a 

 pure dominant or a pure recessive of each of the other two. Each 

 of the character-combinations in Class I occurs on the average in 

 10 plants. 



Class II has 12 terms or character-combinations, each of which 

 is constant for two characters, but inconstant or hybrid in the 

 third. This is illustrated by the combination AABBCc. The sym- 

 bols indicate that the seeds in this combination are round (AA), 

 yellow (BB), and grey-brown in the seed-coats (Cc). But the fact 

 that c is combined with C indicates that we have here not a pure 

 dominant (CC), but a hybrid (Cc). In other words, AABBCc is 

 constant for form and seed-color, but hybrid as to seed-coat color 

 alone (Cc). It will be noticed that the average number of plants 

 per character-combination in Class II is 19. 



