CHAPTER XXII 



VARIATIONS 



General Discussion. — Variations refer to the differences 

 between individual organisms. Variability is the most con- 

 spicuous feature among living beings. There is no organism, 

 simple or complex in structure and function, that is the exact 

 duplicate of another organism. Nature never produces two 

 individuals that are exactly alike. In a field of wheat, corn, or 

 in a group of any of our cultivated or wild plants, however 

 numerous the plants of the group may be, no individual can be 

 found that does not differ in a number of ways from all othei' 

 individuals of the group. (Figs. 464 and 465.) Plants vary in 



Fig. 464. — Heads of Timothy selected from a field of Timothy to 

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



numerous ways. They vary in the shape, color, size and struc- 

 ture of their flowers; in size, color, and structure of fruit; in length, 

 diameter, and structure of stems; in kind, depth, and spread of 

 root systems; in shape, number, structure, and function of leaves; 

 in resistance to disease and drought; and in other ways too 

 numerous to mention. In addition to the numerous variations 

 that are easily recognized, there are variations in cellular struc- 



513 



