1066 
Journal of Agricultural Research 
Vol. XXX, No. 11 
carries an inhibitor for awning which 
is linked with yellow color, and state 
that the third generation tends to 
substantiate the conclusions drawn 
from the study of the second 
generation. They also observed in 
F 2 and F 3 correlation between yellow 
color and the absence of basal scar 
as well as between yellow color and 
absence of basal hairs. 
Fraser {6) discusses the results ob¬ 
tained in the study of crosses, Sixtv- 
Day X Burt and Sixtv-Dav X Early 
Ripe (Burt). He believes that the 
Sixty-Day carries the factor for awn¬ 
ing, but that it is prevented from oper¬ 
ating in the cross by an inhibitor which 
is closely linked with the factor for 
yellow color in the Sixtv-Day variety. 
He attributed the production of awns 
in the first generation to the extent to 
which this inhibitor (I), is dominant 
over its normal allelomorph (i), which 
in turn is probably dependent to a 
large extent on environmental factors. 
He believes that environment influences 
the production of awns and states that, 
though experimental evidence is lack¬ 
ing, increased moisture and fertility of 
the soil tend to decrease their number. 
According to Fraser, the variety Sixtv- 
Dav would have the genetic formula 
for color rryyYY as contrasted with 
the formula RRYYyy of the variety 
Burt. He states further: 
Other workers have shown that the variety Sixty- 
Day carries with it a factor which inhibits the pro¬ 
duction of awns, which factor is closely linked with 
the factor for yellow color. Because of the yellow in 
the variety Burt, which carries no inhibitor, the in¬ 
hibitory effect of the Sixty-Day factor was obscured. 
Fraser says that considerable varia¬ 
tion in kernel color is to be noticed 
even within the same pure line during 
different seasons or under strikingly 
different environments. He speaks of 
Sixty-Day as being a yellow variety 
and found white F 2 plants which failed 
to breed true in F 3 . The difficulty of 
making exact color classification due to 
gradation is also pointed out. Linkage 
was observed between the fully awned 
condition, the presence of midlength 
basal hairs, and the Burt (sterilis) type 
of articulation. 
CHARACTERS OF THE KHERSON 
SPIKELET 
A brief description of the oat spike- 
let is given to make clear the discussion 
of the experiments which follow. The 
principal spikelet characters studied, 
as in previous similar investigations 
by Coffman, Parker, and Quisenberrv 
(4), were spikelet disarticulation, floret 
disjunction, basal hairs, awns, and 
lemma color. 5 
The oat spikelet is borne on the end 
of the pedicel, terminating in the lower 
segment of the rachilla. Each spikelet 
contains two or more florets, of which 
usually only the two lowest are fertile, 
the lower one of the two being the larger 
and longer. The outer or empty glumes 
are thin, membranous, broadly lanceo¬ 
late, pointed, glabrous, and broadly 
arched. The upper is a little longer 
than the lower and both exceed the 
lemma or flowering glume in length, 
except in the hull-less or naked group. 
There are no varieties bearing exclu¬ 
sively one, two, or three kernels per 
spikelet. Two or more usually occur 
and may or may not be separated in 
threshing. The florets are connected 
by the clavate segments of the jointed 
rachilla, each segment of which sup¬ 
ports a single floret. 
SPIKELET DISARTICULATION 
The separation of the spikelet from 
the plant by disarticulation at the 
juncture of the lower floret and its 
supporting rachilla segment has been 
fully discussed in the previous paper 
on "the Burt oat (4). In the present 
study only two distinct forms of 
lemma base resulting from spikelet 
disarticulation were recognized. The 
oval smooth-edged and rather promi¬ 
nent cavity or scar resulting from 
abscission, usually found in oat kernels 
of the Red Rustproof type, was not 
observed in this study of Kherson. 
In the present study, therefore, spikelet 
disarticulation was classed as by semiab¬ 
scission and by fracture. The pointed 
form of base resulting from fracture is 
commonly associated with oats of the 
Avena sativa group. The term semiab¬ 
scission was used for those kernels 
which showed a slight or poorly de¬ 
veloped basal cavity resulting partly 
from abscission and partly from 
fracture. 
FLORET DISJUNCTION 
The manner of separation of the 
kernels of the spikelet varies with the 
species. In some species, as in Avena 
fatua and its derivatives, disjunction of 
the upper floret from its supporting 
rachilla segment takes place in ap¬ 
proximately the same manner as does 
that of the spikelet. In Avena sterilis 
and its derivatives the rachilla and the 
lemma of the upper kernel are solidly 
grown together; the kernels do not 
6 For assistance in determining the morphologic characters of the oat spikelet and for the terminology 
used the writers are greatly indebted to C. R. Ball, senior agronomist in charge of Cereal Investigations. 
