of Heredity 15 



That we are in the presence of a new principle of the 

 highest importance is manifest. To what further con- 

 clusions it may lead us cannot yet be foretold. But both 

 Mendel and the authors who have followed him lay stress 

 on one conclusion, which will at once suggest itself to 

 anyone who reflects on the facts. For it will be seen that 

 the results are such as we might expect if it be imagined 

 that the cross-bred plant produced pollen grains and egg- 

 cells, each of which bears only one of the alternative varietal 

 characters and not both. If this were so, and if on an 

 average the same number of pollen grains and egg-cells 

 transmit each of the two characters, it is clear that on a 

 random assortment of pollen grains and egg-cells Mendel's 

 law would be obeyed. For 25 per cent, of "dominant' 1 

 pollen grains would unite with 25 per cent, "dominant" 

 egg-cells ; 25 per cent. " recessive ' pollen grains would 

 similarly unite with 25 per cent. " recessive " egg-cells ; 

 while the remaining 50 per cent, of each kind would unite 

 together. It is this consideration which leads both Mendel 

 and those who have followed him to assert that these facts 

 of crossing prove that each egg-cell and each pollen grain 

 is pure in respect of each character to which the law 

 applies. It is highly desirable that varieties differing in 

 the form of their pollen should be made the subject of 

 these experiments, for it is quite possible that in such a 

 case strong confirmation of this deduction might be ob- 

 tained. [Preliminary trials made with reference to this 

 point have so far given negative results. Eemembering 

 that a pollen grain is not a germ-cell, but only a bearer of 



nation of the question of the absence of beneficial results on cross- 

 fertilising P. sativum, a subject already much investigated by Darwin, 

 and upon this matter also important further evidence is given in 

 great detail. 



