INHERITANCE IN THE BAELEY SPIKE. 3 
with spikes as lax or as dense as those of the parents, with a series 
lying between these extremes which could not be satisfactorily classi- 
fied without further test. In some crosses the F 2 generation curves 
plotted from the measurements showed two peaks and in others three. 
In a cross of zeocritonX nutans groups of plants were centered about 
internode lengths of 2.2 and 3 millimeters, respectively. The 65 
plants constituting the more dense group were tested in the F 3 
generation by seeding all individuals with internode lengths ranging 
from 1.8 to 2.6 millimeters. Of these 65 plants, 55 proved homozy- 
gous and 10 were heterozygous. Thus, 55 out of a total of 209 plants 
grown in F 2 bred true for densities near that of the dense parent, or 
a close approximation of a 1 : 3 ratio. No genetic analysis is given of 
crosses which appear to have three groups in F 2 , or lax, dense, and 
intermediate forms. 
Study has been made of the inheritance of density in wheat and, 
i although apparently pertinent, it is not comparable to one made in 
barley, for the reason that the dense wheats are clubbed at the tip 
and thus introduce a condition which makes comparison dinicult. 
Gradations were found in F 2 between the parents. Mlsson-Ehle (20) 
explained these on the basis of two kinds of factors, a positive factor 
for compactness which partially inhibited the action of one or more 
lengthening factors. Parker (21), in a more extensive study in which 
the statistical method was used, concludes that numbers such as 
Nilsson-Ehle used were inadequate to demonstrate his hypothesis. 
In Parker's studies segregation occurred in F 2 , but it seemed impos- 
sible to determine the number of factors involved. 
PURE-LINE VARIETIES USED IN THESE STUDIES. 
B With the exception of the Jet variety, the pure lines used in crosses 
in the studies here reported are quite typical representatives of the 
three degrees of density much used by taxonomists in the 6-rowed 
barley. Their relationships are most easily made apparent by use of 
the taxonomic key which follows. The variations in density are well 
shown in Plate I. 
KEY TO BAELEY VARIETIES USED IN DENSITY STUDDZS. 
Hordeum vulgar e pallidum (6-rowed, hulled, awned, white). 
Sub variety typica, spike lax, pure-line Manchuria. 
Subvariety parallelum, spike dense, pure-line Reid Triumph, 
v Subvariety pyramidatum, spike very dense, pure-line Pyramidatum. 
Hordeum distichon palmella (2-rowed, hulled, awned). 
Subvariety nutans, spike lax, pure lines Hanna and Steigum. 
Subvariety erectum, spike dense, pure-line Svanhals. 
Subvariety zeocriton, spike very dense, pure-line Zeocriton. 
Jet is a naked, black, 2-rowed barley of about the same spike 
density as Steigum. Although Hanna and Steigum belong to the 
same group, Steigum is slightly more dense than Hanna. Deficiens 
