Junk, 1920] GENETICS 313 



showed no unbranched progeny, produced in the seventh generation 10 in 340 12 per cent) 

 unbranched individuals with undeveloped panicles (mass mutation). Progeny from these 

 were unbranched in 19 per cent of cases. It is assumed that in the fifth generation a gamete 

 mutated and mated with a normal gamete producing a half-mutant in the sixth which, by 

 splitting, gave the pure mutants in the seventh generation. In the production of albino 

 forms by mass mutation (percentages noted for four species) half-mutants (green forma) 

 are also produced which segregate in Mendelian fashion.— In dioecious and Belf-sterile plants 

 the relationships are more complicated. Seven species were investigated by the writer, 

 especially the self-sterile Linaria vulgaris in which peloric forms appear sporadically in 

 nature. In this case the fifth generation shows 1 per cent of completely peloric forms. As- 

 sume mutated gametes in the third, or earlier generation, half-mutants in the fourth and mu- 

 tants in the fifth produced by half-mutant X half-mutant. Here again half-mutants are 

 recognizable only by their progeny on account of the dominance of the original pure type. 

 An analogous case is that of the production of doubles in Chrysanthemum segetum. — In Mor- 

 gan's investigations upon Drosophila ampelophila over 100 mutations have appeared but in 

 small percentages. Assume premutation to produce half-mutants which when fertilized by 

 half-mutants give rise to mutant types. Premutations or "inner" mutations, are often very 

 complicated but the principle remains the same. The explanation of the original mutation 

 of the gametes is not yet forthcoming. — Paul A. Warren. 



2115. Dudgeon, G. C. The maintenance of the quality of Egyptian cotton. Bull. Imp. 

 Inst. (South Kensington) 16: 160-170. 1918. — Varieties of cotton in Egypt are stated to have 

 arisen from individual plants (possibly mutants) selected for superior qualities and are be- 

 lieved to have bred true until exposed to crossings with other varieties. Cross-pollination 

 and mixing of seed at gins are considered responsible for rapid loss of uniformity, which 

 makes continuation of industry dependent upon appearance, at frequent intervals, of new 

 varieties. Author discusses practical measures for maintaining purity of varieties grown. — 

 T. H . Kearney. 



2116. Duerden, J. E. Breeding experiments with North African and South African os- 

 triches. IV. Increasing the number of plumes : degeneration and restoration. Union of South 

 Africa Dept. Agric. Bull. 7. 39 p., 12 fig. 1918.— Wild ostriches of northern Africa and strains 

 long under domestication in the south, agree in having from 33 to 39 remiges on each wing. 

 The mean for each group falls between 36 and 37, but there is evidence of several distinct 

 biotypes both in northern and southern stocks. These biotypes represent various stages of 

 degeneration. Fortunately one surviving specimen with the original number of 42 primaries 

 has been found and proved to transmit the tendency to high feather production. The author 

 confidently predicts that it will now be possible to disseminate this trait and very materially 

 increase the commercial value of the annual crop of plumes. — C. H. Danforth. 



2117. Duerden, J. E. Some results of ostrich investigations. South African Jour. Sci. 

 15: 247-284. 4 vl-, 4 fig- Nov.-Dec, 1918. — An account of the characteristics, habit , and 

 general biology of the ostrich, with observations on the genetic behavior of various traits, 

 and a critique on the systematic status of Struthio camehts and «S. auslralis. Descended from 

 more fully endowed ancestors, the ostrich is a form in which some intrinsic influences at work 

 in the germ plasm cause successive mutations that tend to be predominantly in one direction. 

 These mutations by short steps are denuding the bird of its plumage and gradually eliminat- 

 ing its wings and toes. While in no sense adaptive, the degenerative changes have not been 

 as yet particularly disadvantageous, but they can not proceed farther without becoming so, 

 and if the present tendency remains unchecked the genus must in a (geologically) short time 

 become incapable of further existence. It is pointed out that this genus offers exceptional 

 material for the study of degeneration from the point of view of genetics. A physiological 

 observation of interest is the fact that the red and blue skin color of the male is due to pres- 

 ence of testes while his black plumage is due to absence of ovaries. — F. G. Danforth. 



