518 



EVOLUTION 



son. Thus if one should select a certain height, a certain num- 

 ber of flowers per plant, etc., as typical of a given species and as 

 standards of comparison, deviations of individuals from these 

 standards are variations. Darwin was a careful student of 



Fig. 465. — Heads of Timothy selected from a field of Timothy to 

 show variation in form and size of heads. After Clark. 



K^-i. 



Fk;. 



lation in Icn-tli of cars select. m1 from a lield of Black 

 Me.xican Sweet Corn. .\ft(>r East. 



variations and observed that variations in structure and func- 

 tion are so common that no two individual organisms are ex- 

 actly alike. In a field of grain or in a group of any of the culti- 

 vated or wild plants no two individuals can be found that are 

 exactly alike (Figs. 1^65 and 1^66). They differ in height, shape, 



