VARIABILITY AND AMPHIMIXIS* 



A Comparative Study of the Variability in Zygo- 

 spores OF Spirogyra in flat a (Vauch.) formed by 

 Lateral (Close breeding) and by Scalariform 

 (Cross breeding) Conjugation, and its Bearing on 

 THE Theory of Amphimixis and Correlated Prob- 

 lems. 



I. Preliminary outline 98 



1. Introduction 



2. Historical 



3 . Material 



4. Methods 



II. Consideration of results 105 



1. Comparative variability in length of zygospores 



2. Comparative variability in diameter of zygospores 



3. Comparative correlation between length and diameter 



4. Comparative size of zygospores 



III. Discussion of results 109 



1. Comparative variability 



2. Comparative size 



3. Comparative correlation 



4. Origin of amphimixis and of death 



IV. A working hypothesis of evolution 119 



V. Conclusions 121 



VI. Bibliography 123 



I. Preliminary Outline 



1 . Introduction 



Comparative studies along statistical lines of the results 

 produced by cross breeding and close breeding afford 

 data of value bearing on the problem of evolution as well 

 as the subsidiary problem of the origin of amphimixis. 

 It has long been assumed (Weismann, '76) that sex existed 

 primarily to increase variability and with the further as- 

 sumption that the variations thus produced were heritable 

 and accumulated, the differentiation of organisms was 

 logically explained. As a corollary to such a conclusion 

 the belief has long been prevalent that the offspring of 



*Reprinted from The American Naturalist, vol. 49 (1915), pp. 649-687. 



