LEE BARKER WALTON 93 



organisms produced by cross breeding were as a group 

 more variable than those produced by close breeding, an 

 idea which gained further acceptance in connection with 

 the investigations of Castle ('06), Jennings ('08, '09, '12, 

 *13) and others interested in problems of genetics. That 

 there was excellent evidence for exactly an opposite view 

 and that an analysis of the results presented by the in- 

 vestigators mentioned above did not bear out the conclu- 

 sion that variability was increased by cross breeding has 

 been pointed out by the writer (Walton, '08, '12, '14) in 

 some earlier papers. 



The importance of arriving at a correct conclusion con- 

 cerning the part played by hybridization and cross breed- 

 ing in evolution can not be overestimated. If units are 

 merely redistributed and form characters resulting in no 

 actual evolutionary progress, work along Mendelian lines 

 tends rather to obscure the facts of value toward solving 

 the problem of the origin of species as well as that of evo- 

 lutionary control in animal and plant breeding. It is 

 therefore well to obtain data from as many sources as 

 possible bearing on the question. 



Among the species of Spirogyra, a group of algae be- 

 longing to the class Conjugatae, there are several which 

 reproduce both by lateral conjugation where the adjacent 

 cells of a single filament unite to form the zygospore, 

 itself a young individual, and at the same time by scalari- 

 form conjugation where the cells of two distinct filaments 

 unite to form the zygospore. Thus there is an example 

 of a population producing under the same environment 

 two groups of individuals, one by close breeding (lateral 

 conjugation) and the other by cross breeding (scalariform 

 conjugation) , and a comparison of the variability by 

 statistical methods should afford evidence toward the 

 solution of the problem presented where the offspring 

 have arisen from a common ancestor as indicated in the 

 material studied. 



2. Historical 



Much has been published concerning hybridization, 

 cross and close breeding, amphimixis and parthenogene- 

 sis, all of which are distinguishable from one another 



