Vol. 7, 1921 GENETICS: SETCHELL ET AL. 51 
tails involved in character differences within the species. Accordingly 
three crosses were actually made and studied at some length. In some 
cases derivative lines were carried into the tenth hybrid generation. The 
three crosses, all in reciprocal, were made in 1909 as follows: (1) angusti- 
folia x macrophylla, (2) calycina x virginica (Maryland) and (3) alba 
(White) x macrophylla. Detailed descriptions of the above-named varie- 
ties have been given by Setchell 3 in a previous paper. In this article we 
shall confine our attention to the Mendelian results of the studies. 
The Angustifolia-Macrophylla Series. — In the angustifolia-macrophylla 
series an attempt was made to subject two character differences to Men- 
delian analysis, viz., the light pink flower color of angustifolta versus the 
red of macrophylla and the long-petioled leaf-base of angustifolta versus 
the sessile, broad leaf-base of macrophylla. The former of these contrasts 
proved to be a simple monogenic one, but the latter necessitated a complex 
Mendelian formulation. 
Turning our attention to flower color first, Fi was pink-flowering but 
the intensity of coloration was distinctly greater than that of angustifolia. 
Ten F 2 families containing a total of 490 plants consisted of 377 pink- 
flowering and 113 red-flowering plants. The pink-flowering segregants 
clearly gave evidence of the existence of two sub-classes differing in in- 
tensity of coloration. The count totalled 240 pink-flowering and 137 
light pink-flowering individuals, a rough approximation to a 2 : 1 ratio. 
Very little reliance, however, can be placed upon this classification be- 
cause of the evident intergrading of the two sub-classes. Separation into 
red and pink was clear and distinct. The F 3 populations conformed to 
expectation based upon the F 2 results, with the single exception noted 
below. Four F 2 red-flowering selections gave 99 F 3 plants all red-flowering. 
Of fifteen F 2 pink-flowering selections ten gave progenies exhibiting segre- 
gation in conformance with the 3 pink : 1 red ratio, the actual totals being 
187 pink: 60 red. Four F 2 pink-flowering selections bred true for pink, 
the entire 89 F 3 plants being pink. One population from an F 2 pink- 
flowering selection yielded a progeny consisting entirely of red-flowering 
plants. It is difficult to state whether this result indicates a misclassi- 
fication of the F 2 parent or whether some other experimental error was 
to blame for it. Taken as a whole the data adequately establish the mono- 
genic nature of the pink : red character contrast. Light pink is to be 
considered as incompletely dominant over red, and the genetic differ- 
ence may be designated by the symbols R for light pink and r for red. 
The analysis of the leaf -base difference proved to be rather complicated. 
Fi was petioled, but the petiole was shorter than that of angustifolia 
and the wing of the petiole was more amply developed. In F 2 a hopelessly 
complex series of forms was obtained ranging from extremely long-petioled 
to very broadly sessile types. Although it was impossible to demonstrate 
any valid Mendelian distribution in F 2 , it was possible to distinguish 
