Unit Characters 147 



been already implied, we do not know how a new 

 factor comes to be, but we know a good deal about 

 the "sorting-out" of factors once they are there. The 

 reality of "factors" is but little affected by their 

 invisibility. There is no doubt as to the reality of 

 the unseen virus of some diseases. 



"Unit-characters" may be illustrated by eye-color 

 (which never seems to blend), by night-blindness 

 (which has persisted in the Nougaret lineage since 

 Charles I was King), by the Hapsburg lip (in the 

 royal houses of Austria and Spain), and by brachy- 

 dactylism (having fingers all thumbs). To illustrate 

 the heterogeneity, we may continue the list among 

 plants and animals. It includes hornlessness in cattle, 

 crests in poultry, Angora hair in rabbits, albinism 

 and waltzing in mice, pink eye in fruit-flies, yellow 

 seeds in peas, immunity to rust in wheat, six-rowed 

 ears in barley, serrated margins in nettle leaves, be- 

 sides subtle features like early ripening in cereals or 

 broodiness in poultry. All these peculiarities illus- 

 trate Mendelian inheritance. 



It is still an open question whether Mendelian in- 

 heritance is the universal mode, or whether the di- 

 vergent characters of the parents may sometimes 

 blend in the offspring so that intergrades result. 

 There are cases which suggest this, but it must be 

 recognized that an apparent "blending" may come 

 about when an adult character depends on numerous 

 factors. If some of the factors come from the mother 

 and others from the father an appearance of blend- 

 ing may result. Another question, not to be closed as 



