58 MODES OF RESEARCH IN GENETICS 



have arisen in any individual instance. A first 

 study in this direction was made by the writer 

 for variation in the plant Ceratophyllum. 1 More 

 recently fundamental researches of a similar 

 character have been made by Jennings on varia- 

 tion in Paramecium. In the writer's laboratory 

 a study has lately been made, from this point of 

 view, of the inter-individual (racial) variation 

 curves of one of the higher plants. 2 The first 

 necessity in all such analytical studies must be 

 a precise description and definition of the things 

 which are to be analyzed. Such a description the 

 application of biometric methods furnishes. 



In what has been said regarding biometry as 

 a method of group description, reference has been 

 made, for the sake of simplicity of illustration, to 

 groups of individual organisms. The same 

 considerations, however, apply with equal or 

 perhaps ever greater force to the study by bio- 

 metrical methods of groups of like parts or organs 

 within the single individual. Appropriate quan- 

 titative methods make it possible to detect and 

 analyze the most subtle phenomena of differen- 

 tiation in the development and growth of the in- 

 dividual. In the absence of methods for dealing 

 with a group of parts or individuals as such, one 



1 Carnegie Institution of Washington, Publication No. 58, 1907. 



2 Pearl, R. and Surface, F. M. "Growth and Variation in 

 Maize." Zeitsch. f. ind. Abst.- u. Vererbungslehre, Bd. XIV, pp. 97- 

 203, 1915. 



