318 GENETICS [Bot. Absts. 



2138. Hayes, H. K., and E. C. Stakman. Rust resistance in timothy. Jour. Amer. Soc. 

 Agron. 11:67-70. 1919. — At Minnesota Exp. Sta. in 1917 authors collected data from one 

 hundred and twenty-five plants on rust resistance of eight Minnesota selected strains and 

 eleven Cornell University improved strains of timothy (Phleum pratense). In a rust epidemic 

 induced by spraying the second growth with spores of Puccinia graminis Cornell strains 

 showed a high percentage of resistant plants while Minnesota strains were very susceptible. 

 Investigation was discontinued after 1917. Authors conclude that a rust resistant timothy 

 may be easily produced, and think that breeding for disease resistance is often a local prob- 

 lem. They believe that closer cooperation between investigators attacking the same prob- 

 lem would be of national significance. — J. Ben Hill. 



2139. Hegner, R. W. Heredity, variation, and the appearance of diversities during the 

 vegetative reproduction of Arcella dentata. Genetics 4: 95-150. 27 fig. Mar., 1919. — Arcella 

 dentata has many obvious advantages for genetic study, for example, spine number and shell 

 diameter are not modified by growth and environmental factors after division is completed. 

 It was found that the hereditary constitution of different families obtained by vegetative 

 reproduction from different "wild" specimens differs with respect to spine number, prob- 

 ably a vast number of such heritably diverse families occurring in "wild" populations. By 

 selection in 22 generations during 64 days two lines were obtained from a single specimen 

 reproducing vegetatively, showing an increasing difference between their mean spine num- 

 bers as selection progressed. This divergence persisted through 35 days (18 generations) of 

 non-selection and is regarded as permanent. Further, halves of the low line were subjected 

 to 23 days (15 generations) selection, followed by 11 days non-selection, with similar result. 

 These divergent subfamilies correspond in heritable characteristics to small families derived 

 from many "wild" individuals. Parallel results were obtained for mean shell diameter of 

 above-mentioned high and low lines and high and low branches of low line. There is signifi- 

 cant correlation between spine number and shell diameter. In one instance a sudden large 

 variation ("mutation") in spine number and shell diameter appeared in low line. It was 

 markedly smaller and had fewer spines than other specimens of low line and "bred true." 

 From this branch 3 distinct branches having larger specimens with more spines than any 

 other branch of the selection family appeared. Empty shells were often produced by appar- 

 ently normal specimens but had no influence upon heritable diversities studied. — A large 

 family of Arcella dentata, derived from a single specimen by vegetative reproduction, was split 

 by selection into heritably diverse branche- as regards diameter and spine number. These 

 resemble hereditarily diverse families obtained by- vegetative reproduction from "wild" 

 specimens. The formation of such hereditarily diverse branches appears to be a true case of 

 evolution that has been observed in the laboratory and that occurs in a similar way in nature. 

 — A. R. Middleton. 



2140. Henry, Augustine, and Margaret G. Flood. The history ef the Dunkeld 

 hybrid larch, Larix eurolepis, A. Henry, with notes on other hybrid conifers. Proc. Roy. 

 Irish Acad. 35: 55-66. PI. 11. 1919.— A full description of the anatomical characters of the 

 hybrid and the two parent species, Larix leptolepis and L. curopaea, is given. The remark- 

 able difference in the epidermal cells of the leaves of the European and Japanese larches — the 

 surface of the former smooth, of the latter roughened with papillae — is connected with the 

 fact that the Japanese tree bears considerably more shade than the European species. The 

 papillose epidermis allows much light to penetrate the epidermis, and be available for photo- 

 synthesis. In the non-papillose epidermis most of the light is reflected, and is lost to the 

 leaf as far as photosynthesis is concerned. In the hybrid only t' e cells on the central part of 

 each surface of the leaf bear papillae; the rest of the epidermal cells are smooth. L. eurolepis 

 grows with astonishing vigor, much surpassing either of the parents. A hybrid hemlock 

 spruce, Tsuga Jeffrcyi A. Henry, native of Mount Baker in British Columbia, and of the 

 mountains behind Cowichan Lake, Vancouver Island, is also described. — Aug. Henry. 



