50 



Miitahility and Individual Variation. 



meaning the differences between individuals, and the 

 latter the equally frequent differences between the organs 

 of a single individual. 



The necessity of distinguishing between variability 

 in space and time has been often insisted upon;^ I mean 

 between (a) the diversity in a group of forms existing 

 at the same time, and (b) the differences existing between 



K% tZJ 13 13Z Tt ns IS ISj 10 ItiJ 17 17.5 18 I3.S (9 



Fig. 12. Amount of Sugar in Beets, at Naarden." 



On January 24, 1896. 



— On January 25, 1896. 



On January 28, 1896. 



parents and their children, and more distant descendants. 

 Ploetz has proposed that contemporary varying indi- 



^ W. Waagen, Die Formcn des Ammonites suhradiatns in Be- 

 necke's Geognostisch-Palaontologische Beitriige, 1876, Bd. II, p. 1S6. 



^ The three curves exhibit the sugar contents of beets from one 

 large sample taken from three successive determinations on January 

 24th, 25th and 28th, 1896, by exactly the same method. The num- 

 bers in each lot were 6848, 6781 and 6191, amounting almost to 

 20,000 polarizations. The sugar contents varied from about 12 to 

 19 per cent. These figures I owe to the generosity of Messrs. Kuhn 

 & Co., the owners of the factories at Naarden. — In spite of the con- 

 siderable number of values taken the curves do not exactly coincide. 

 The third curve taken 3 days later has its apex shifted a little to 

 the right. The differences between the 2 others are obviously to 

 be attributed to unavoidable chance circumstances. In the compari- 

 son of empirical curves with theoretical ones, a closer agreement 

 than that between 2 curves from 2 samples of the same kind must 

 obviously not be expected. For theoretical purposes therefore one 

 should, where possible, compare two or more curves of the same 

 phenomenon. 



