500 



BIOLOGY AND HUMAN LIFE 



for Luther Burbank's thornless blackberry. A grain stalk may 

 appear without the sharp bristles among the grains ( see Fig. 213). 

 A seedless plum or a seedless orange grows unexpectedly upon 

 a tree that had previously borne only respectable fruit with 

 seeds. These sudden departures from parental types of plants 

 or animals are called mutations. They differ from mutilations, 



Fig. 212. The Ancon type of sheep 



There are no known descendants of the famous Ancon ram that appeared in Massa- 

 chusetts in 1 79 1. The animal shown in the picture has the short legs and long body 

 of that sport, but it was born from apparently normal parents on a Norway farm in 

 19 19, and was found by Nils Thorshaug, the live-stock ofiicer. One of her daughters is 

 of the same type; the other descendants are normal. (Photograph by Director Baeroe 

 of the Jonsberg Agricultural School, Norway). (Courtesy of Dr. Christian Wriedt) 



or from the effects of overfeeding or other conditions in the 

 surroundings, in breeding true, that is, in giving rise to offspring 

 like themselves. Where mutations have desirable qualities, 

 they are preserved for further breeding. 



!: In modern times the breeders of plants and animals have not 

 been content with finding desifable plants and animals by 

 chance, with having them introduced occasionally from abroad, 



