m MENDEL'S WORK 23 



plants, and since the dwarf character has been entirely 

 eliminated from them they must in the future breed true. 

 The latter must also give rise to tall plants, but since they 

 carry also the recessive dwarf character they must when 

 bred from produce both tails and dwarfs. Each of the 2 x 

 dwarf ovules, again, has an equal chance of being fertil- 

 ised by a "tall" or by a "dwarf" pollen grain. Hence 

 X will give rise to tall plants carrying the recessive dwarf 

 character, while x will produce plants from which the tall 

 character has been eliminated, i.e. to pure recessive dwarfs. 

 Consequently from the 4X ovules of the self -fertilised 

 hybrid we ought to obtain 3 x tall and x dwarf plants. 

 And of the 3 x tails x should breed true to tallness, while 

 the remaining 2 x, having been formed like the original 

 hybrid by the union of a "tall" and a "dwarf" gamete, 

 ought to behave hke it when bred from and give tails and 

 dwarfs in the ratio 3:1. Now this is precisely the result 

 actually obtained by experiment (cf. p. 17), and the close 

 accord of the experimental results with those deduced 

 on the assumption of the purity of the gametes as enun- 

 ciated by Mendel affords the strongest of arguments for 

 regarding the nature of the gametes and their relation to 

 the characters of the zygotes in the way that he has done. 

 It is possible to put the theory to a further test. The 

 explanation of the 3 : i ratio of dominants and recessives 

 in the Fj generation is regarded as due to the Fj individ- 

 uals producing equal numbers of gametes bearing the 



