THUMB-FINGERNESS 51 



experiment, for since there has been no intermarrying 

 each one has had one parent abnormal and the other 

 parent normal. 



It follows that when one of these abnormals (com- 

 parable to the hybrid plant) marries a normal, their 

 children should be of both kinds ; one half should 

 show the abnormality and the other half not. 



As a matter of fact, 52 per cent, of the offspring 

 of abnormals have been normals, and as there is 

 always in such cases an element of chance, this per- 

 centage is held to be a sufficiently close approximation 

 to theoretical requirements. 



Mendel found that the dwarf plants when self- 

 fertilised, or bred amongst themselves, always breed 

 true to the dwarf character, and not only so, but that 

 the dwarfs of the third generation (one of whose 

 parents was tall) invariably breed true and produce 

 nothing but dwarf plants. Further than this, if the 

 first hybrids (tall) are bred amongst themselves or are 

 self- fertilised, they produce a certain proportion of 

 dwarfs (25 per cent.), and even these dwarfs breed 

 true to dwarfness. 



These dwarf plants, from a hereditary point of 

 view, correspond to the normal members of the short- 

 fingered family. Such being the case, a norma! 

 person (one of whose parents is short-fingered) ought, 

 when married to another normal, to produce normal 

 children only, and this has been the invariable result. 



If the chart is consulted, it will be seen that the 

 normals (represented by small letters) have not in a 

 single instance had short-fingered children. The 



