MUTATIONS 



265 



factor mutation has a certain effect upon every character in the organism, 

 yet the visible effects of some factor differences are restricted to a single 

 character. According to their visible effects, therefore, we recognize two 

 classes of factor mutations: (1) those conditioning apparently only single 

 characters; (2) those having a visible manifold effect on the soma. Cases 



FIG. 110. A seedling of the oak-like walnut (left) and of the California black walnut, 



the parent species (right.) 



involving mutations of the second class are known in several species of 

 animals and plants. An interesting example is the oak-like walnut, 

 Juglans calif ornica var. querdna, which appears to differ from the parent 

 species by a single factor difference, Fig. 110. But this variety is distinct 

 from the species type in nearly all gross morphological characters. 



