314 GENETICS [Bot. Absts. 



21 IS. Duerden, J. E. Crossing the North African and South African ostrich. Jour. 

 Genetics 8: 155-198. PI. 7, 2 fig. June, 1919.— Hybrids between North and South African 

 ostriches are intermediate between the two parents except that baldness of the northern 

 form is completely dominant. The limited data indicate that in F 2 various original traits 

 tend to segregate in true Mendelian fashion. Blending in Fi is attributed to interaction in 

 the hybrid germ plasm of homologous, but still not quite identical, genes. In this paper 

 the author still further elaborates his view that in all ostriches, perhaps in the Ratitae as a 

 whole, there is some inherent degenerative tendency that manifests itself through successive 

 small mutations, affecting particularly feathers, wings and toes. Emphasis is laid upon the 

 point that, while the usual evolutionary conception of mutation is one of fortuitous discon- 

 tinuity, studies of the ostrich show that "discontinuous changes in the individual may pro- 

 ceed along definite lines and result in determinate continuous evolution for the race as a 

 whole."— C. H. Danforth. 



2119. Easle a, Walter. Mildew resistant roses: with some suggestions as to increasing 

 their number. Jour. Roy. Hortic. Soc. 43 : 253-260. 1919.— Author notes that many of our 

 present hybrid varieties owe their weakness to one or the other of the parents. Urges more 

 care in selecting of resistant parents, also growing of seedlings from desirable varieties which 

 are resistant. Gives list of varieties which are more or less mildew-resisting. [See Bot. 

 Absts. 3, Entry 2256.]— C. E. Myers. 



2120. East, E. M. Studies on self-sterility. III. The relation between self-fertile and 

 self-sterile plants. Genetics 4: 341-345. July, 1919.— Summary of the self-sterility (of the 

 type due to physiological incompatibility) and the self-fertility of hybrids between the so- 

 called self-sterile species Nicotiana Forgetiana and N. alata with the self-fertile species N. 

 Langsdorjfii. The Fi are reported to be all self-fertile. Of the F 2 , of one cross 144 were self- 

 fertile and 38 self-sterile; from the other cross 200 were self-fertile and 38 self-sterile. The 

 F 3 grown from self-sterile plants of the F 2 are reported all self-sterile. The genetic difference 

 between self-sterile and self-fertile plants in these species is ascribed to the presence and ab- 

 sence of a single determiner for self-fertility. The discrepancies in ratios are considered to 

 be due to "pseudo self-fertility." Variations in the development of "pseudo self-fertility" 

 are reported and these are assumed to be due to another factor or factors which dilute the 

 action of sterility due to the absence of the factor for fertility. — A. B. Stout. 



2121. East, E. M. Studies on self-sterility. IV. Selective fertilization. Genetics 4: 

 346-355. July, 1919. — Test for selective fertilization in hybrids between the two decidedly 

 3elf-sterile species Nicotiana Forgetiana and N. alata, made by comparing variability in the 

 rate of pollen-tube growth of compatible crosses among an F 2 with that of sib matings of the 

 Fs. Data presented for five sections of pistils of each of the two sorts show no significant 

 differences in the two cases. — A. B. Stout. 



2122. East, E. M. Studies on self-sterility. V. A family of self-sterile plants wholly 

 cross-sterile inter se. Genetics 4: 356-363. July, 1919. — Results of a further study of cross- 

 incompatibilities in a family derived by crossing a plant of Nicotiana alata (9) with an Fi 

 plant (d") of N. Forgetiana X N. alata. Of a considerable number of crosses only 13 combina- 

 tions produced capsules and seeds. The successful cases are ascribed to pseudo cross-fer- 

 tility and the family is considered as fully self-sterile and cross-sterile. Due to origin of 

 family and the behavior of a sister family the condition is difficult to explain on assumption 



.of a homozygosity for factors of sterility. — A. B. Stout. 



2123. Erdmann, R. Endomixis and size variations in pure lines of Paramoecium aurelia. 

 Proc. Soc. Exp. Biol. Med. 16: 60-65. 1919. — Author refers to work of Jennings on selection 

 in Paramecium and Difflugia, and discusses the relation of endomixis to the formation of 

 heritably diverse lines in Paramecium during asexual reproduction. She decides that endo- 

 mixis "acts as a stabilizer and effaces the fluctuations around the mean, that Jennings had 

 seen in his cultures." The conclusion is reached that endomixis also gives rise to new com- 

 binations that can be selected and is thus an "originator of new lines." Directed selection 

 can thus isolate -heritably diverse lines in an asexually propagated organism. — R. W. Ilegner. 



