xSa Referate. 



Daebishire, a. D. Breeding and the Mendelian Discovery. Cassell & Co., 

 London. 1911. XII + 282 S. 34 figures and 4 coloured plates. 



The author of this book describes its object as being to put before 

 the practical breeder of animals or plants the facts in Heredity which may 

 be of use to him. The method adopted is thus somewhat different from 

 that used in most books on heredity; the first part of the book deals 

 almost exclusively with matters of direct observation and the theoretical 

 explanation of the facts is postponed to the later chapters. This method 

 has the undoubted advantage of giving first actual ascertained facts which 

 can hardly fail to arouse the interest of practical men; the account is 

 generally clear and readable and is admirably illustrated with diagrams 

 and photographic figures which are both simple and beautiful. The method, 

 however, has the disadvantage of involving a certain amount of repetition; 

 partial explanations are unavoidable in the earlier chapters, and must be 

 repeated and amplified later. 



The subject is opened with a description of the observations of de Vries 

 on mutation in Ocnotlicra. Mendelian inheritance is introduced by an 

 account of the characters studied by Mendel himself in the Pea-plant, 

 the seed characters being left until the simple animal cases of the Anda- 

 lusian fowl and human eyecolour have been considered. A simple case of 

 reversion (waltzing mouse crossed with albino) is followed by the explanation 

 of dihybridism and the 9:3:3:1 ratio as seen in peas and the combs of 

 fowls. This leads naturally to a further explanation of reversion and to 

 the "presence and absence" theory. The separation of the account of 

 reversion into two distinct chapters in the first part and a third in the 

 later part of the book illustrates the r'ifficulty referred to of avoiding 

 repetition. The author admits the truth of the "presence and absence" 

 theory in some cases, but declines to commit himself as to its general 

 validity, a position typical of his attitude towards all generalisations which 

 are verifiable in some cases but not at the present time in all. The last 

 chapter in what may be regarded as the first part of the book gives 

 instructions for practical workers with plants. 



The later part of the book deals chiefly with the theoretical explanation 

 of Mendelian facts, and is generally clearly written with apt illustration, 

 but the author's subtle and at times almost hypercritical attitude of mind 

 towards explanation as distinct from fact may be confusing to some to 

 whom the subject is unfamiliar. An interesting chapter deals with the 

 relation of Mendel's discovery to earlier, contemporary, and later biological 

 thought. The failure of Nägeli to appreciate its importance is discussed, 

 and the author points out how close the relation is between j\Iendelism 

 and Weismannism, although Weismann was unacquainted with Mendel's 

 work. A reproduction (4 pages) is given of the letters in the Horticultural 

 Society's Transactions of 1822 by John Goss, who had observed in peas 

 the facts of dominance, segregation, and the true-breeding of recessives, 

 but failed to arrive at Mendel's explanation. 



The last two chapters deal with the relation between Mendelian in- 

 heritance and sex, and are less satisfactory than the rest of the book, for 

 the author is clearly less familiar with the subject. The inheritance of 

 horns in sheep is described as "sex-limited", and the author says that the 

 mode of transmission of colourblindness in man "would appear to be exactly 

 the same", thus neglecting the fundamental difference that the colourblind 

 man transmits the affection {or rather its "factor") only to his daughters, 

 while the horned ram transmits the factor for horns to his offspring of 



