26 GENETICS [BoT. Absts., Vol. VII, 



while there is evidence that double ovulation is relatively common, the probability that 

 viable twins will be produced is dependent upon the chance that both ova will be fertilized 

 and that both will be free from lethal factors. These prerequisites are dependent as much 

 upon the sperm as upon the egg and it is known that fecundity and the presence or absence 

 of lethal factors are hereditary traits. — C. H. Danforth. 



178. Davis, Bradley M. [Rev. of Gager, C. Stuart. Heredity and evolut'on in plants. 

 U X 20 cm., xi + 265 p., IIS fig. P. Blakiston's Son & Co.: Philadelphia, 1920.] Science 

 52: 410. Oct, 29, 1920. [See Bot. Absts. 6, Entry 1672.] 



179. Dembowski, Jan. Das Kontinuitatsprinzip und seine Bedeutung in der Biologie. 

 [The principle of continuity and its significance in biology.] Vortr. u. Aufsatze ii. Entwick- 

 lungsmech. Org. 21. 132 p. 1919. 



180. Dexter, John S. Albino vertebrates. Science 52: 130-131. Aug. 6, 1920.— The 

 author makes note of a pure albino grackle (Quiscalus quisctda aeneus), two albino speci- 

 mens of Richardson's spermophile (Citellus richardsoni) , and a very light brown albinistic 

 crow. — Sewall Wright. 



181. [Diener, Richard.] The law of hybridizing discovered by Richard Diener. 20 X 26 

 cm., 15 p., 8 fig. Richard Diener, Kentfield, California. [1920.] — Author claims to have 

 made the following discoveries: (1) AVhen parents are alike in size, the size of about 12 per 

 cent of the offspring in the Fi will be exactly double that of either parent, while the remain- 

 ing 88 per cent will range in size between the size of the individual parents and their sum. 

 (2) When parents differ markedly in size, the offspring will be smaller than either parent 

 if the smaller parent is the mother, and very little larger than the larger parent if the latter 

 is the mother. (3) The pollen-bearing parent is always the dominating factor in changes of 

 form and color. (4) In attempting to derive new colors always use a white flower as .the 

 pollen parent "to break up the colors." (5) Among fowls, if two individuals are mated 

 and the female offspring are mated back to the male parent, about one-third of the offspring 

 of this second cross will be double the size of the animals originally mated. Basis of these 

 generalizations are not specifically set forth. — G. H. Shull. 



182. Dreyer, Th. F. A suggested mechanism for the inheritance of acquired characters. 

 South African Jour. Sci. 15:272-277. 1917. — Author attempts to show that observed facts 

 supporting Weismann's theory are meager — that acceptance of theory by younger genera- 

 tion is partly a matter of sentiment. The character and properties of chromatin, lymph, 

 and linin are reviewed. The linin being divided equally at cell division is considered as 

 hereditary material on a par with the chromatin. A metabolic-products theory of heredity 

 assumes the egg yolk to be specific for species, and assumes that it is a linin compound 

 formed from radicals of the various tissues of the body. Reactions occur in different portions, 

 so that it is not homogeneous; segmentation can thus split off different combinations of 

 radicals which are built up into different tissues. Environmental factors may cause some of 

 these radicals in the tissues to change so that the new yolk formed from the tissue radicals 

 will contain new radicals from the altered tissues. Thus acquired characters could be repro- 

 duced in the next generation in the absence of the causative stimulus. — /. L. Collins. 



183. DuERDEN, J. E. Parallel mutations in the ostrich. Science 52: 165-168. Aug. 20, 

 1920. — Ostriches are degenerate in some respects, but highly specialized in others. The 

 North African Ostrich {Struthio camelus) and the South African {S. australis) differ in well- 

 marked characters, at least one of which (feathering of head) is believed to be a simple Mende- 

 lian character. In other respects they are similar, and the author believes parallel evolution- 

 ary changes are in progress in them. The similarity in this respect is attributed to parallel 

 mutations in germ -plasms of common origin. The suggestion is made that while the majority 

 of factors are static, some may be increasing in potency while others are dwindling. — L. J. 

 Cole. 



