328 



The Journal of Heredity 



that become established in many spe- 

 cies. But in addition to these larger 

 differences the internode individuals of 

 the same type show a general diversity 

 corresponding to that of individual 

 plants or animals which are members 

 of the same species. Thus the most 

 direct indications of biological facts do 

 not support the idea of definite paths 

 of development, or of paths that are 

 followed exactly. The inference is 

 that diversity, rather than uniformity, 

 should be considered as the normal 

 product or manifestation of heredity. 

 The different types of internodes of 

 the same plant were considered by 

 Goethe as an important evidence of evo- 

 lution, and a like significance may be 

 claimed for internode diversity in rela- 

 tion to heredity. 



Having seen that the expression of 

 characters is frequently and indefinitely 

 varied in the development of the inter- 

 node individuals, it seems not unrea- 

 sonable to expect a similar variability 

 in sexually produced individuals, and 



to consider such diversity as a result of 

 normal reproductive processes. Goethe 

 described the growth of internodes, 

 one from another, as "successive re- 

 production," in contrast with "simul- 

 taneous reproduction" by sexual pro- 

 cesses. 



Notwithstanding the great advances 

 that have been made in recent years in 

 the cytological study of transmission 

 and the mechanical explanation of the 

 inheritance of Mendelian differences, 

 there still is no conception of the nature 

 of the characters, as showing how they 

 are represented in transmission, or how 

 they are brought into expression. 

 Hence it is possible as yet to think 

 definitely of characters only as they 

 are brought into expression, through 

 the development of the plant or ani- 

 mal individual. The results that are 

 produced are the only basis of judg- 

 ment regarding the nature of the repro- 

 ductive processes, the transmission and 

 expression of the characters. 



A Survey of the Whole Field 



Readings in Evolution, Genetics, 

 AND Eugenics, by Horatio Hackett 

 Newman, Professor of Zoology in 

 the University of Chicago. Pp. 253, 

 with 1 01 illustrations ; price $3.75- 

 University of Chicago Press, 1921. 



That this volume has passed through 

 several impressions since its first pub- 

 lication, is good evidence that it meets 

 a need of the collegiate world. It con- 

 sists of extracts from the works of 

 standard biological writers, living and 

 dead, together with numerous introduc- 

 tions and discussions by Professor 

 Newman, covering all the important 

 phases of the subjects included in the 

 title. The sections dealing with what 

 arc now more or less historical aspects 



of genetics are full enough to leave the 

 uninitiated reader in some doubt, per- 

 haps, as to just how far they have 

 stood the test of criticism, and subse- 

 quent development of the subject. It 

 is perhaps inevitable that some topics 

 should be dealt with by writers who 

 are by no means recognized as masters 

 of them, though perhaps eminent in 

 some other field of biology. Difficulties 

 like these are certain to occur in any 

 book made of selected readings, and if 

 thev require elucidation, the instructor 

 will doubtless he able to supply it. On 

 the whole, the book is probably the 

 most useful single volume available to 

 a reader seeking merely a brief account 

 of all aspects of genetics. — P. P. 



