16 GENETICS [BoT. Absts., Vol. X, 



linked inheritance, and intersexuality are explained. Sex determination takes place either 

 before, at, or after fertilization. Exceptions to Mendel's laws are found in reversible domi- 

 nance, fluctuation of unit characters, and irregular ratios; these have been explained by aux- 

 iliary hypotheses, such as inhibiting factors, linkage, repulsion, reduplication, differential 

 mortality, incompatibility, etc. The Mendelian theory is in harmony with the corpuscular 

 theory of Weismann, mutation theory, genotype theory, and evolution and selection theory. 

 The author thinks it probable that continuous variation of germ-plasm occurs under the 

 effect of environment and selection; in unicellular organisms it always results in visibly con- 

 tinuous variations, while in multicellular ones the results may appear as discontinuous varia- 

 tions. — Section V. Many characters are shown to depend on physiological features of embry- 

 onic development; complexly determined characters are more likely to exhibit impure 

 segregation than simple ones; difference is attributed to ferments; characters complex in de- 

 velopment are more likely to be of selective value. Extreme cases of complex causation may 

 be highly species-specialized; intermediate cases are species-forming characters. Characters 

 found in many species are usually simple in development and inheritance. Simple characters 

 in man persist in hybrid races, complex ones tend to disappear. The inheritance of numerous 

 human traits is described. — Section VI. Individuality of chromosomes is no longer to be 

 regarded as a working hypothesis, but as a well-grounded theory. The author doubts the cor- 

 rectness of the theory of parasynapsis and splitting of chromosomes as accounting for forma- 

 tion of tetrads, holding that these phenomena may be partly due to accident, and partly to 

 artifact; but he recognizes that Mendelian heredity is better explained by that theory than bj' 

 telosynapsis. The Suttox-Boveri chromosome theory of heredity is outlined. The chro- 

 mosome theory of sex is considered almost universally accepted. Some form of quantitative 

 theory fits the facts better than the hypothesis that there are specific genes for sex as for other 

 characters; but both theories are objectionable. The author believes that X chromosomes 

 are mere indices, not causes; the relation of metabolism to sex supports the index-hypothesis. 

 Proof of Morgan's theories of linear arrangement and crossing over await discoveries in forms 

 in addition to Drosophila. Purity of gametes is proved, but that segregation is effected by 

 reduction division is still in doubt; there is much evidence of somatic segregation. The 

 author suggests the nucleoplasma theory to account for unequal cell divisions, including 

 segregation of genes. Materials passing from the nucleus to the cytoplasm, or produced in 

 the cytoplasm under the influences of the nucleus, may be equally divided at cell division, or 

 may be sorted out (segregated); these substances may in turn influence the nature of the 

 nucleus. Quantitative relations are supposed to determine dominance. — Final Section. 

 Though a knowledge of Mendelian phenomena has led to few striking improvements in domes- 

 ticated animals, it has made intelligible many puzzling phenomena, such as instability of 

 certain species, atavism, individual potency, effects of inbreeding, heterosis, limits of artificial 

 selection, and correlation, and has been useful in anthropology. — A. Franklin Shull. 



93. Harlan, H. V., and S. Anthony. Development of barley kernels in normal and 

 clipped spikes and the limitations of awnless and hooded varieties. Jour. Agric. Res. 19: 

 431-472. 1920. — Removal of awns at flowering time results in (1) a lessened deposit of dry 

 matter in the kernel, especially of starch; and (2) an increased deposit of ash in the rachis of 

 the spike. The awn functions as a depository for ash and its removal causes the surplus ash 

 to accumulate in the rachis. This ash accumulation causes brittleness of the spike and con- 

 sequent tendency to shatter. Hooded and awnless sorts have rachises more brittle than 

 armed sorts, also yield less grain. The production of high-yielding strains of these types 

 may be possible by using parents having a low percentage of ash in the rachises. — The substi- 

 tution of smooth for scabrous armed sorts is suggested as likely to meet the objections of 

 growers and feeders of barley. The production of such sorts equal in yield to the latter is a 

 future task of the plant breeder. — F. P. Bussell. 



94. Harrison, J. W. Heslop. The variation of Primula farinosa L. in County Durham. 

 Vasculum 7: 21-25. 1921. — Variations are described in P. Jarinosa found in the mountains 

 and along the Durham coast. Many of the variations are similar to those attributed to 

 hybridization. The isolation of desirable types is attributed to the isolation of factors 

 hitherto latent. — Karl Sax. 



