LEE BARKER WALTON 103 



duction. In a subsequent part of the present paper a 

 somewhat critical review of the data and conclusions 

 therein noted is presented. 



3. Material 



In obtaining material early one April for the labora- 

 tory work of a class in biology, the collection being made 

 in a small pool resulting from the overflow of a rivulet, a 

 peculiar species of Spirogyra was noticed in which both 

 lateral and scalariform conjugation was taking place often 

 in the same filament. It was at once suggestive that a 

 comparison of the variability in the two groups of zygo- 

 spores would present facts of interest in connection with 

 the effect of close breeding and cross breeding on varia- 

 bility as well as affording evidence as to the theories of 

 amphimixis. 



The species was first determined as Spirogyra qiiadrata 

 (Hass.) but subsequent examination indicated that it 

 should be classified as Spirogyra in f lata (Vauch.). 



The material utilized for the measurements was all pro- 

 cured at one time from a restricted area one or two inches 

 square on the surface of the pool and included only the 

 one form of Spirogyra, that alone being present as a mass 

 3 or 4 inches in diameter. Inasmuch as both lateral and 

 scalariform conjugation occasionally took place in the 

 same filament a suggestion that two species were repre- 

 sented can not be made for the filaments are alike in every 

 characteristic. Of the 500 zygospores observed 45 per 

 cent were produced by lateral conjugation. 



4. Methods 



In considering the variability of large numbers of 

 microscopic forms, rapid and accurate measurements are 

 a necessity. Pearl and Dunbar ('03) in measuring Ar- 

 cella used a camera lucida, marking the dimensions by 

 means of a needle point, and reducing to microns. Pearl 

 ('06) adopted a similar method for CMomonas, using a 

 magnification of 689.7. Pearl ('07) in measuring Para- 

 mecitim used a 2/3 -inch objective and a No. 1 ocular. By 

 means of a camera lucida the points to be measured were 



