FACTOR RELATIONS IN QUANTITATIVE INHERITANCE 175 
and consequently continue growth until checked by unfavorable external 
conditions or by the drain of seed production. It is, therefore, possible 
in this case to state definitely upon what a size difference depends. 
In sweet peas there are two distinct dwarf forms which display a 
simple type of inheritance when crossed with tall forms. One of these 
types is the Cupid sweet pea which originally arose as a mutation from 
Emily Henderson, a tall white variety. The Cupid sweet pea is a very 
dwarf procumbent type which produces no erect stems. When crossed 
with tall varieties it gives tall plants in F; and in F», segregation into 
Fic. 82.—(right) Young bush bean plant showing determinate habit of growth. The 
axis is terminated by a flower cluster; (left) young pole bean plant showing indeterminate 
habit of growth. The flowers are all in the axils of the leaves. (After Emerson.) 
tall and dwarf in the ratio 3:1. The other restricted form is the bush 
sweet pea. It is characterized by a profuse production of thin, wiry 
branches which intertwine and form a bush, sometimes three and a 
half feet high. Bush crossed with tall gives in F; tall plants and in Fo, 3 
tall: 1 bush. The bush sweet pea, therefore, like the Cupid differs from 
the tall sweet pea in a single genetic factor, and in both cases the tall 
form is completely dominant. 
An interesting situation arises when bush sweet peas are crossed with 
Cupid sweet peas. From our knowledge of the inheritance exhibited 
by these two forms when crossed with tall, we may assume as in previous 
cases that in the appearance of the Cupid mutation there was a change 
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