514 VARIATIONS 



tures recognizable only by the aid of the microscope. 'Even on 

 the same plant there are no two organs exactly alike. The 

 flowers, fruits, leaves, and other organs of the same plant show 



.19 20 21 



FIG. 465. Variation in length of ears selected from a field of Black 

 Mexican Sweet Corn. After East. 



numerous variations. (Fig. 466.) The individuals of each 

 generation not only differ from each other but also from their 

 parents, grandparents and all previous ancestors. Among 

 animals, variations are no less universal than among plants. 



Variations and origin of new forms. The possibility of the 

 origin of new forms of plants and animals by means of evolution 

 rests upon variations. If the individuals of each generation of 

 plants and animals were exact duplicates of the individuals of 

 previous generations, new forms would be impossible. It is gen- 

 erally believed that the first organisms were unicellular and that 

 all other forms have come from these. But it is clear that with- 

 out a variation resulting in multicellular organisms, all living 

 beings would still be one celled organisms. Through variations 

 resulting in multicellular organisms and in the differentiation of 

 cells into various kinds of structures, the more complex organ- 

 isms have originated from the simpler ones. In tracing the ori- 

 gin of the various kinds of plants and animals, we are tracing a 

 series of variations. 



Classes of Variations. Variations may be classified in a 

 number of ways. They may be structural, having to do with 

 differences in the structure of flowers, fruit, leaves, stem, or any 



