CLASSES OF VARIATIONS 515 



other organ, or they may be functionaj, having to do with the 

 amount of food leaves make, the amount of fruit produced, the 

 amount of absorption by the roots, etc. Some variations are 

 useful and some harmful to the individual while there are others 

 that are neither useful nor harmful. Variations may also differ as 

 to origin. Some of the variations which individuals have are 

 due to modifications in the sex cells of the parents of the indi- 

 viduals. Such variations are due to something inherited. The 



FIG. 466. A number of leaves and fruits selected from the 

 Oak tree to show variation in form. After Hayden. 



majority of variations are not due to anything inherited, but are 

 simply modifications of leaves, flowers, fruit, stems, etc., due to 

 environmental influences. Some variations, known as fluctuating 

 variations, fluctuate around a standard that remains practically 

 the same throughout generations. Variations which are merely 

 differences in structures and functions due to environment are of 

 this kind. Some variations, known as mutations, are such wide 

 departures in characters that new standards are established. 

 Variations may or may not be hereditary and this classification 



