HEREDITY 151 



Darwin emphasized the great importance of continuous 

 or fluctuating variations. He says, " It may be doubted 

 whether sudden and considerable deviations of structure 

 such as we occasionally see in our domestic productions, 

 more especially with plants, are ever permanently prop- 

 agated in a state of nature. Almost every part of every 

 organic being is so beautifully related to its complex 

 conditions of life that it seems as improbable that any 

 part should have been suddenly produced perfect, as 

 that a complex machine should have been invented by 

 man in a perfect state." 



Sudden variations were called by Darwin discontinuous. 

 Variations frequently occur which vary widely from 

 the parent form. Examples of this kind of variation 

 are common in both plants and animals. The normal 

 fruit of a peach tree is a typical peach having a rough 

 skin and a flavor and color peculiar to the peach. 

 Branches of peach trees, however, sometimes produce a 

 fruit known as a nectarine. This is smooth, smaller 

 than the peach, and possessed of a color, flavor and physical 

 consistence markedly different from the normal fruit of 

 the peach. 



Among animals mutations frequently occur. Varia- 

 tions in the number of digits have been recorded by a 

 large number of investigators. Huxley describes the 

 case of a man born with six fingers on each hand and six 

 toes on each foot. Four children were born to this man. 

 The first, a male child, was born with six fingers on each 

 hand and six toes on each foot. The second child, a 

 boy, had five fingers and five toes, but one toe was de- 

 formed. The third child, also a boy, had five perfect 

 fingers and toes, but the fourth child, a girl, although 

 having the normal number of digits, had deformed thumbs. 



