An Introduction to a Biology 



at once ; they produce dwarfs only. Of the three tails in 

 the second hybrid generation, one, at the left of the diagram, 

 breeds true ; it produces tails only, so it may be called a 

 pure tall. The two remaining tails — the two in the middle 

 of the second hybrid generation — each produce tails and 

 dwarfs in the proportion of 3 to 1 — that is to say, they behave, 

 in their breeding, exactly as do the hybrid tails of the first 

 hybrid generation, and we may therefore call them hybrid tails. 

 The facts shown in Fig. 1 may therefore be condensed 

 into the following diagram : — 



Pure Tall x Pure Dwarf 



I 

 Hybrid Tall 



1 Pure Tall. 2 Hybrid Tails. 1 Pure Dwarf. 

 or — 



Pure Tall x Pure Dwarf 



Hybrid Tall 



I I 



^5% Pure Tall. 50% Hybrid Tall. 25% Pure Dwarf. 



We will deal with points to be noticed in Fig. 1 in order 

 of their importance, beginning with the least important. 



It will be seen that the dwarf character entirely dis- 

 appears in the first hybrid generation. The tall character 

 completely dominates over it ; the tall character is therefore 

 called the dominant character, and the dwarf character is 

 called the recessive character. And the two characters, tall- 

 ness and dwarfness, constitute a Mendehan pair of cha- 

 racters. I have repeated the word " character " in the pre- 

 ceding hues often, in order to lay stress on the fact that 

 dominance and recessiveness belong to a particular cha- 

 racter, and not to the plant as a whole. 



The second point to be noted in Fig. 1 is that the 



264 



