PROCEEDINGS OF THE OHIO ACADEMY OF SCIENCE 123 



Attempts were subsequently made to obtain data bear- 

 ing on the results of close breeding and cross breeding 

 which differ merely in degree from parthenogenesis and 

 amphimixis. The question is an important one for if cross 

 breeding is only valuable in sorting out and combining 

 existing characters, it not only obscures the facts, a knowl- 

 edge of which is necessary before progress can be made in 

 building up new characters, but results in no actual 

 advancement in cumulative evolution. Here the material 

 for study consisted of scalariform or cross bred, and lateral 

 or close-bred (parthenogenetic) zygospores — in reality the 

 young individuals — of the common filamentous green alga 

 Spirogyi'a inflata (Vauch). Upon applying statistical meth- 

 ods the close bred zygospores were found to be 33 per cent, 

 more variable"^ in size as well as larger, both in length and 

 actual volume, than the cross bred zygospores. The results 

 were not in accord with the general belief that cross breed- 

 ing increased variability, although studies by Warren, Kel- 

 logg, and Casteel and Phillips had pointed out that this 

 belief was not substantiated by facts, which however did 

 not actually warrant the idea that variability was decreased 

 in cross bred forms. The studies on the zygospores also 

 suggested that sex existed primarily for the purpose of 

 limiting variability, an hypothesis proposed on purely theo- 

 retical grounds by Hatschek in 1887. Another conclusion 

 from the same investigation was that in connection with 

 the origin of death"* and which may be mentioned here. 

 This may be summarized by stating that death apparently 

 occurs as the result of the continually forming body cells 

 becoming so variable through absence of control by amphi- 

 mixis that eventually some one group of functional impor- 

 tance fails to meet the limits imposed by the environment. 

 In consequence of this the group together with the remain- 

 der of the colony — the individual — perishes. 



2 Science, p. 907, 1908. 

 =* Science, p. 935, 1912. 



