138 CARNEGIE INSTITUTION OF WASHINGTON. 



mother, as contrasted with 1.8 for 1919, 1.6 for 1917, and 2.2 for 1916. 

 It is thought that this falling-off in percentage of twin births is due, in 

 part, to the youth of the ram and, in part, to the poor nutritive condi- 

 tions in which the ewes were found at tupping time. The cooperative 

 sheep experiment with the New Hampshire Experiment Station, 

 which experiment is primarily under the direction of Mr. E. G. Ritz- 

 man, is being continued. A joint paper by Ritzman and Davenport, 

 "A comparison of some traits of conformation of Southdown and Ram- 

 bouillet sheep and of their Fi hybrids," was pubhshed during the year. 



During the year about 80 chicks of the Silky and rumpless strains 

 were hatched. Dr. George B. Jenkins made further studies on rump- 

 lessness and abnormal plumage of these strains. 



Professor H. D. Fish, of Denison University, Research Associate at 

 the Station, has made use of the facilities of the Station during the year 

 to continue his remarkable series of rabbits which are being bred, 

 largely, to get at the factors for spotting and coat color. 



HEREDITY IN MAN. 



Studies on this topic by members of the station are considered under 

 the Eugenics Record Office. 



SPECIES HYBRIDS. 



More and more, in both plants and animals, the subject of sterility 

 and the importance of lethal factors, factors that kill, is assuming great 

 prominence. This leads to the subject of sterility between distinct 

 species. As a guest of the Station, Mr. John Belling has been paying 

 special attention to the nature of species hybrids in plants and the mode 

 of inheritance of their characters, especially of partial sterility. Mr. 

 Belling is working especially on the genus Can7ia, which contains nu- 

 merous species that are propagated as clones. It appears that most 

 of the Canna clones are heterozygous and much affected by imperfect 

 pollen-grains, which can be readily distinguished from those that are 

 perfect. The topic has important theoretical bearings on the origin of 

 species, since distinct species are usually characterized by some degree 

 of sterility. 



GERMINAL AND SOMATIC VARIATIONS. 

 MUTATIONS IN MUCOR. 



A report on mutations by Dr. Blakeslee in vegetatively pure lines of 

 mucors is in press. In addition to a number of mutants of various 

 types already reported, one mutant from a hermaphrodite has been 

 cultivated in pure vegetative lines since 1913, but has consistently 

 failed to show sexual spores since its first discovery. That it is still a 

 hermaphrodite is obvious by its sexual reactions with both test plus (+) 



