Recombination in Species Crosses.

N THE field of mathematics there are numerous problems difficult to I solve with finite numbers which become relatively simple when the concept of infinity is introduced, Similarly, though the genetics of species crosses is obscure when considered in terms of single factors, i t seemed possible that i t might be illuminated if one attempted to consider the total recombination of specific differences. The recombinations in any particular cross could be compared, as a whole, with the particular species combinations from which they arose, or the total recombination in one cross compared with that in another. Such an experiment with Nicotiana Langsdorfii and N . alata was started in 1930 at the John Innes Horticultural Institution. It was carried forward at the Missouri Botanical Garden the following year and a t the Bussey Institution of Harvard University from 1931 to 1933 while the author was a staff member of the Arnold Arboretum. Grateful acknowledgment is made to these institutions and to DR. HENRY W. EDMONDS and MRS. RUTH OWNBEY for faithful and expert assistance in collecting the data and preparing i t for publication. I am indebted to DR. PRISCILLA AVERY of the University of California for unpublished information in regard to chiasma frequencies. A preliminary account was presented a t the Sixth Genetics Congress (ANDERSON 1932)~ and the chief conclusions were incorporated in a technique (ANDERSON 1936) for the study of hybrid populations. Publication in extenso has been deferred until the conclusions could be checked experimentally with other genera and until certain phases of the work (ANDERSON 1939) could be given a more complete statistical treatment. Though the method is simple it leads to somewhat unexpected conclusions. It furnishes new criteria for the recognition and analysis of hybridization in natural or artificial populations and should prove of practical assistance to the plant breeder.