442 BOTANICAL GAZETTE [MAY 



the correctness of WEISMANN'S contention that "body and germ-cells are physio- 

 logically distinct," and that "body (or somatic) influences are not inherited." 

 The next six chapters deal with "the greatest single discovery ever made in the 

 field of heredity, Mendel's law," with illustrations drawn chiefly from the 

 author's experiments with guinea-pigs, rabbits, rats, and mice. After a careful 

 statement of the general principles with concrete examples, attention is given 

 to the determination of dominance, heterozygous characters and their "fixa- 

 tion," atavism or reversion, evolution by loss or gain of characters, evolution 

 of new races by variations in the potency of characters, modification of unit- 

 characters by selection, and "blending" inheritance. This enumeration of the 

 subjects treated suffices to indicate that the author's discussion is no merely 

 formal presentation of the ramifications of the Mendelian system. Instead, it 

 deals lucidly and entertainingly with a number of moot questions. It is pleas- 

 ing to note that the author does not follow some other recent writers (BATESON, 

 PUNNETT, DAVENPORT) in the view that dominance is always due to the pres- 

 ence of a gene which is absent from the recessive form. He mentions several 

 cases for which this explanation is not available, and leaves the problem as 

 to the cause of dominance unsolved. He is convinced that unit-characters 

 may be modified by selection. He says (p. 120): "In several cases I have 

 observed characters at first feebly manifested gradually improve under selec- 

 tion until they became established racial traits." While this must be accepted 

 as an observed fact, the statement that it is due to selection is apt to be mis- 

 leading. The difficulty remains that selection can only pick out individuals 

 already possessing the observed degree of development of any characteristic 

 under consideration, and does not in any manner modify the qualities which 

 will be possessed by the offspring of the selected individuals. It only permits 

 such individuals to reproduce to the exclusion of other individuals which do not 

 have the x character in question. Under "blending inheritance" the now well- 

 known case of skull-size and ear-length in rabbits is discussed, and the view 

 is expressed that in the light of experimental results of NILSSON-EHLE, EAST, 

 and others, such cases of apparent blending may really prove to be segregating 

 inheritance in which a considerable number of units are involved. 



In chap, ix the effects of in-breeding are considered, and the reviewer's 

 conception is indorsed, that the apparent deterioration is generally due to the 

 formation of homozygous strains, whereby the stimulus is lost which comes 

 from the "bringing together of differentiated gametes, which, reacting on each 

 other, produce greater metabolic activity." In this connection the statement 

 is made (p. 150) that "under self-pollination for one generation following a 

 cross, half the offspring become homozygous; after two generations three- 

 fourths of the offspring are homozygous"; and so on. This statement is 

 misleading as it stands, and is literally true only in the case of monohybrids. 

 A second cause recognized for deterioration following in-breeding is the ap- 

 pearance of recessive defects, such as albinism, etc., a cause which has been 

 specifically pointed out by DAVENPORT. 



