BEARERS OF HEREDITARY CHARACTERS 235 



progeny. Then hybridization produces nothing new ? Mendel, 

 and plant breeders before and after him have obtained results 

 that are quite otherwise. Hybridization does in fact give rise 

 to more new varieties than have been obtained in any other way. 

 In our consideration of hybrid peas, for the sake of keeping the 

 main point in view, we ignored the fact that plants are a complex 

 of many characters, and that any two varieties taking part in a 

 cross would be apt to have more than one pair of characters 

 contrasting. In fact Lawrence Balls calls attention to twenty- 

 three pairs of such characters in cotton visible to the naked eye, 

 and beyond question there are many others of this kind besides 

 those that are obscure and invisible. 



In the two varieties of peas; flowers terminal and flowers 

 lateral made a pair of contrasting characters, and if one of our 

 plants had long leaflets and the other had short, this would give 

 another contrasting pair. Under such conditions Mendel's 

 experiments showed that all possible combinations of characters 

 occurred in the offspring of the hybrid, provided these were 

 numerous enough to give all combinations a chance of appearing. 

 It was found that the number of these combinations might be 

 estimated by the formula x = 2", where x stands for the number 

 of combinations sought, and n stands for the number of pairs of 

 contrasting characters. In our example above, the value of n 

 would be 2, and the number of possible combinations would 

 therefore be 4, and of the following character; terminal flowers 

 with short leaflets, terminal flowers with long leaflets, lateral 

 flowers with short leaflets, lateral flowers with long leaflets. 



Bearers of Hereditary Characters. — ^When we seek for an 

 explanation of these results in processes going on within the 

 heredity bearers or chromosomes we find ourselves on hypothet- 

 ical ground, but where, nevertheless, a survey of possibilities 

 may reveal to us the right conclusion. We may start with the 

 assumption that each chromosome is the bearer of more than 

 one hereditary character, because plants certainly possess many 

 more characters than chromosomes, and, furthermore, there is 

 clearly a greater diversity in chromosome numbers than in 



