i6 BREEDING 



the ancestry of the second hybrid generation, we find 

 only one kind of dwarf — a pure, true-breeding or 

 stable kind ; but we find two kinds of tails, a pure 

 stable kind which produces tall offspring only, and 

 a hybrid or unstable one which produces both tall 

 and dwarf. 



What, then, is the nature of the three tails of 

 the second hybrid generation ? There are three 

 possibilities. They may be all pure ; or all hybrid ; or, 

 lastly, some of them may be hybrid and some pure. 

 This latter is actually the case. Two of the three 

 are hybrid, and produce tails and dwarfs in the 

 ratio of three tall to one dwarf in every four. The 

 remaining tall is pure, and produces only tails. 



In the genealogical table we have supposed that 

 each plant of the second hybrid generation produces 

 only four offspring, because this enables us to put 

 the average proportions of tails and dwarfs amongst 

 these offspring most conveniently in diagrammatic 

 form. The pure tall which produces only tails is 

 seen at the extreme left of the second hybrid genera- 

 tion. In the middle are the two hybrid tails, each 

 producing three tails and one dwarf on the average ; 

 and at the extreme right is the dwarf, which produces 

 only dwarfs. 



Let us now glance at the actual proportions 

 observed by Mendel himself. He does not say how 

 many plants of the first hybrid generation he raised ; 

 he only states that he made thirty-seven crosses 

 between tall and dwarf. We do not, therefore, Imow 

 how many of these were successful. His second 



