SHORTER ARTICLES AND DISCUSSION 



VARIABILITY UNDER INBREEDING AND CROSS- 

 BREEDING 



An unusually thoughtful and suggestive discussion of evo- 

 lutionary problems is contained in Professor Walton's paper on 

 "variability and amphimixis" published in the November, 1915, 

 number of this journal. But the paper is in some danger of 

 neglect because the conclusions reached are apparently so revo- 

 lutionary that to a casual reader they may seem freakish. Yet 

 it will be seen by one who reads the paper more carefully that 

 the radical character of its conclusions is due in part to the fact 

 that certain familiar ideas are here viewed at a new angle. 

 Nevertheless the new point of view has, it seems to me, to some 

 extent, caused the author loss of perspective in relation to some 

 of the phenomena which he discusses, for which reason further 

 consideration of them may be profitable. 



The occasion of Walton's discussion was a biometric study 

 which he made of two sorts of zygospores produced by Spirogyra 

 inflata, one sort produced by union of cells in the same filament 

 (called by him "close fertilization"), the other by the union of 

 cells in different filaments (called "cross fertilization"). Zy- 

 gospores of the former sort ("close fertilized") were found to 

 be on the average larger and more variable than those of the 

 latter sort, contrary to the prevailing idea that cross fertiliza- 

 tion leads to increased variability. It may however be ques- 

 tioned whether Walton's material is such as to throw new light 

 on this question, for it is by no means certain that cells of 

 Spirogyra which unite in lateral conjugation are the exact 

 equivalents morphologically and physiologically of those which 

 unite in scalariform conjugation. It is conceivable that zygo- 

 spores formed in lateral conjugation may be larger and more 

 variable because the cells which gave rise to them were as a 

 group larger and more variable. It is conceivable that cells 

 which resort to scalariform conjugation are not such as can 

 satisfy their physiological demands for conjugation by uniting 

 with a sister-cell in the same filament. For it is known that in many 

 plants sexual union occurs only as a last resort, when conditions 

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