INHERITANCE ON CROSSING 51 



of dwarfs in this generation bore a constant proportion 

 to the whole. On countings there were found to be 

 about 25 per cent, dwarfs, or one dwarf to every three 

 tails. 



On further breeding it was found that the dwarf 

 plants, if left to themselves, produced only dwarf off- 

 spring — they " bred true," as we say. Here, then, was 

 something new, and something which at first seemed 

 paradoxical. A perfectly dwarf plant is produced by a 

 perfectly tall parent, and the offspring of this dwarf 

 are all, without exception, dwarfs like itself. 



When the tall plants of the second generation were 

 left to produce seed by themselves, and the seed of 

 each plant was grown separately, it was found that some 

 produced only tall offspring, whereas others, like their 

 parents, produced both tails and dwarfs. There must, 

 then, have been two kinds of tall plants in the second 

 generation, some which were " pure " in the same 

 sense as their dwarf brothers, others which were " im- 

 pure " in the sense that they did not produce ex- 

 clusively tall offspring. It was found that among the 

 groups of offspring there were very nearly two mixed 

 lots to each pure lot, showing that in the second genera- 

 tion there must have been two " impure " tall to each 

 " pure " tall. The mixed groups of offspring consisted, 

 on the average, of 75 per cent. taUs, 25 per cent, dwarfs. 



T 



The above scheme may perhaps help to explain 

 these results. In it, the letter T represents the tall 

 condition, D the dwarf. We will suppose only four 



D 



