568 THE PROBLEMS OF HEREDITY AND THEIR SOLUTION. 



"dominant''' egg' colls; ^6 per cent " reces.sivo" pollen grains would 

 similarly unite with 25 per cent "recessive'' eg-g- 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 g'rain is pure in respect of each character to which the law 

 applies. It is highly desirable that varieties ditiering in the form of 

 their pollen should l)e made the subject of these experiments, for it is 

 quite possi])le that in such a case strong conlirmation of this deduction 

 might be obtained. [Preliminary trials made with reference to this 

 point have so far given negative results. Remeiubering that a pollen 

 grain is not a germ cell, but only a bearer of a germ cell, the hope of 

 seeing pollen grains differentiated according to the characters they 

 bear is probably remote. Better hopes may perhaps be entertained 

 in regard to spermatozoa, or possibly female cells.] 



As an objection to the deduction of purity of germ cells, however, 

 it is to be noted that though true intermediates did not generally occur, 

 yet the intensity in which the characters a})peared did vary in degree, 

 and it is not easy to see how the hypothesis of perfect purit}^ in the 

 reproductive cells can ])e supported in such cas(^s. Be this, however, 

 as it may, there is no doubt we are beginning to get new lights of a 

 most valuable kind on the nature of heredity and the laws which it 

 obeys. It is to be hoped that these indications will be at once followed 

 up by independent workers. Enough has been said to show how 

 necessary it is that the subjects of experiment should be chosen in such 

 a way as to bring the laws of heredity to a real test. For this pur- 

 pose the tirst essential is that the differentiating characters should be 

 few, and that all avoidable complications should be got rid of. Each 

 experiment should be reduced to its simplest possible limits. The 

 results obtained by (ialton, and also the new ones especially described 

 in this paper, have each l)een i-eached by restricting the i-ange of 

 observation to one character or groUp of characters, and it is certain 

 that by similar treatment our knowledge of heredity may be rapidly 

 extended. 



To the above popular presentation of the essential facts, made for 

 an audience not strictly scientiffc, some addition, however l)ri(>f. is 

 called for. First, in regard to the law of ancestry, spoken of on a 

 preceding pag(^ Those who are acquainted with Pearson's Gi'ammar 

 of Science, second edition, published early in 1900, the same author's. 

 paper in Proceedings Royal Society, volume Q6, 1800, page l-tO, or the 

 extensive memoir (published October. IHOO), on the inheritance of 

 coat color in horses and e3'e color in man (Phil. Trans., 11)5, A, 1900,, 

 p. 79), will not need to be told that the few words I have given above 

 constitute a most impcn-fcct diagram of the operations of that law as 

 now developed. Until the appearance of these treatises it was, 1 



