LEE BARKER WALTON 109 



the diameter is approximately the same. This is illustrated 

 in Table VIII. 



Consequently, here, the average zygospore produced by 

 lateral conjugation has a greater volume than that pro- 

 duced by scalariform conjugation. Utilizing the formula 

 for computing the volume of a prolate spheroid (V = 

 l/67rld'~) the difference is 771 cubic m. in favor of the 

 former, although relatively this approximates only 3 per 

 cent. 



A question of some interest is at once suggested, namely, 

 the possibilities for nourishment and development in cells 

 of large and of small volume, inasmuch as one with a 

 maximum volume has relatively less surface through 

 which nourishment may be obtained. Thus growth may 

 be retarded. 



III. Discussion of Results 



The close bred forms on the basis of the characters 

 studied in the given population have been found more 

 variable as to both length and diameter, more highly 

 correlated, and larger taking into consideration length 

 and volume. The value of the conclusions in their ap- 

 plication to the solution of problems of evolution is de- 

 pendent on the logical application of cause and result as 

 well as the methods of the investigation. 



That the two groups of zygospores are comparatively 

 close bred and cross bred will scarcely be denied, par- 

 ticularly when it is remembered that in lateral conjuga- 

 tion nearly all adjacent pairs of cells in a filament had 

 united in the process, each pair producing a zygospore, 

 all pairs having originated from the same cell. With 

 the material taken from a part of a mass a few centi- 

 meters square, a sample of a whole population has been 

 utilized, and from what is known of the reproduction of 

 Spirogyra, it may be assumed with reasonable certainty 

 that the entire mass had its origin from zygospores pro- 

 duced in a few filaments the preceding year. With 

 practically all zygospores measured in each filament, the 

 criticism that isolated zygospores of mixed descent were 

 studied, and that greater variability would be expected in 



