266 Varietäten, Descendenz, Hybriden. 



Walton, L. B., Variability and amphimixis. (American Na- 

 turalist. IL. p. 641—687. 1915.) 



As direct conclusions, resulted from his researches, the writer 

 summarizes: 



1. Zygospores of Spirogyra inflata (Vauch.) produced by lateral 

 conjugation or close breeding (quasi-parthenogenesis) are relatively 

 26 per cent. more variable in iength and 31 percent. more variable 

 in diameter as measured by the coefficient of Variation, than those 

 produced by scalariform conjugation or cross breeding (sexual 

 reproduction). 



2. The size (volume) is greater in the average (mean) zygospore 

 close bred by lateral conjugation, where the mean Iength is 62.38 ^u 

 + 0.178, than in the average zygospore cross bred by scalariform 

 conjugation, where the mean Iength is 60.44 n ±_ 0.135. The diame- 

 ter is approximately the same in both types. 



3. In zygospores produced by lateral conjugation there exists a 

 positive correlation between Iength and diameter of 0.1894 : 0.0460, 

 while in scalariform conjugation the value is 0.0934 : 0.0473. This is 

 in general agreement with results obtained by others although here 

 the difference is not significant when the probable error is considered. 



4. In the material studied approximately 45 per cent. of the 

 zygospores were formed by lateral conjuction, the remaining 55 

 per cent. by scalariform conjugation. 



5. The material studied was strictly homogeneous being inter- 

 mingled with no structural differences except those of conjugation. 

 Consequently the differences in variability are not the result of 

 fluctuability. 



The indirect conclusions run as follows: 



1. Amphimixis, cross-breeding, etc., decreases and does not 

 augment variability (cumulability) although amphimutability may 

 temporarily be increased. 



2. Close bred forms are more highly correlated in respect to 

 related characters than crossbred forms. 



3. Variations, so far as their origin is concerned, may be sepa- 

 rated into A) Normations consisting of 1) fluciuations, 2) amphimu- 

 tations and 3) cumulations and into B) Abnormations consisting of 

 1) malsegregations, 2) defactoriations, 3) fractionations, and 4) mal- 

 formations. 



4. Cumulations may best be investigated among organisms 

 produced asexually, by pure lines, or by close breeding than by 

 cross breeding, etc. 



5. Sexual reproduction and cross fertilization have been advan- 

 tageous in the evolution of organisms by limiting cumulability and 

 thus confining the progress of the group to a path bounded by the 

 more permanent evironment. 



6. Death occurs as a result of the continually forming body 

 cells becoming so variable ihrough the absence of control by am- 

 phimixis, that eventually some one group fails to meet the limits 

 imposed by the environment and these together with the remainder 

 of the colony- the individual-perish. 



As hypotheses the writer gives the foUowing opinions: 



1. Variability (cumulability) will be greater in a small and iso- 

 lated Population than in a large and less isolated population. 



2. Progressive evolution has resulted from factors arising through 

 cumulations without reference to amphimutations (Mendelian com- 

 bination.s). 



