482 



SCIENCE 



[N. S. Vol. XXX. No. 771 



biologists to the newly rediscovered discover- 

 ies of Mendel, but at the present time a book 

 with a wider scope is needed and it has been 

 supplied by the author. 



The present work omits the controversial 

 features of its predecessor, which happily are 

 no longer required, but adds in Part II. some 

 interesting biographical material and three 

 portraits to the translation of Mendel's orig- 

 inal papers which the earlier book contained, 

 and gives a comprehensive account of the de- 

 velopment of Mendelian principles of heredity 

 down to the present year. It may be regarded 

 as an authoritative statement of Mendelism at 

 the present time. No small part of the book 

 is taken up with an account of the author's 

 own investigations, which have probably added 

 more to our present knowledge of heredity 

 than has come from any other source since 

 Mendel's time. 



Chapter I. contains a brief account of pre- 

 Mendelian writings on heredity, of the redis- 

 covery of Mendel's law, and of the essential 

 feature of that law, " segregation." 



Chapter II. contains a list of observed cases 

 of Mendelian inheritance, with the name of 

 the observer in each case and bibliographic 

 references to his work, and a statement of its 

 most important features. The fact is empha- 

 sized that in animals and in plants, and both 

 among domesticated and among wild forms, 

 the laws of heredity are the same. The nature 

 of " dominance " and the occurrence of dis- 

 tinctive heterozygous characters are topics 

 also considered here. Regarding dominance, 

 the conclusion is reached that " a dominant 

 character is the condition due to the presence 

 of a definite factor, while the corresponding 

 recessive owes its condition to the absence of 

 the same factor." 



A critical comparison is instituted between 

 the Mendelian system and Galton's system of 

 analyzing the facts of inheritance, and the 

 inadequacy of Galton's system is shown. 

 Praise is bestowed upon Galton for his early 

 attempts to break a path through the unex- 

 plored fields of heredity, but his followers are 

 censured for persistently closing their eyes to 

 the fact that Mendel has opened a path. 



In a third chapter explanation is made of 

 the usual Mendelian "ratios," 3:1, 9:3:3:1, 

 etc., and an account is given of how novelties 

 may arise, by recombination of the separate- 

 factors of compound characters. Examples 

 from breeding-experiments with fowls, prim- 

 roses and sweet-peas serve as illustrations. 



The next five chapters, about a fourth part 

 of the book, deal with color-inheritance in 

 plants and animals. This is no undue amount 

 of attention, since the phenomena here dealt 

 with are the most carefully studied and the 

 most instructive of all Mendelian cases. 



In this part of the book are discussed and' 

 illustrated the modified Mendelian ratio- 

 9:3:4, the " presence and absence hypoth- 

 esis," epistatic and hypostatic factors, rever- 

 sion on crossing, and a variety of related 

 topics of greater or less complexity. 



A chapter on "genetic coupling and spurious 

 allelomorphism " precedes and leads naturally 

 to a discussion of " heredity and sex." The 

 theory is here advocated that sex has its onto- 

 genetic origin in gametic differentiation, that 

 in each species of animal or plant one sex is 

 heterozygous, the other homozygous as regards 

 the differential sex-factor. In the cases studied 

 by experimental breeding methods the author 

 concludes that " the female is a sex-heterozy- 

 gote with femaleness dominant," whereas the 

 male is a homozygous recessive. The possibil- 

 ity is, however, admitted that in insects, such 

 as have been studied by Wilson, Morgan and 

 others, the male may be the heterozygous sex, 

 as the cytologioal evidence suggests. 



Double flowers and their peculiar inheri- 

 tance are considered in a special chapter, fol- 

 lowing which comes what to many will be the 

 most interesting chapter in the book, " Evi- 

 dence as to Mendelian inheritance in man." 

 Eye-color and hair-color are shovtm to be in- 

 herited in typical Mendelian fashion, though 

 the evidence is admittedly incomplete. Skin 

 color, in the ease of the mulatto at least, seems 

 to be inherited without segregation. Various 

 hereditary diseases and maKormations are 

 sho-wn to be inherited as Mendelian dominant 

 characters. Brachydactyly, cataract, color- 

 blindness and a variety of other hereditary 



