factor, and the derivation of A. sativa from either would 
require an additive mutation. 
Avena sterilis 
The wild red oat is distinguished by having the lower 
floret of a spikelet articulated, while the upper florets are 
not. When the upper florets are separated by fracturing 
the rachilla, most of the rachilla segment remains attached 
to the floret above. This character was used by Cosson 
as the basis of his series Biformes. 
Like the C-factor of A. sativa, genetical studies have 
shown this Biformes character to be due to a single domi- 
nant gene, here called the B-factor. Tschermak (1929) 
reported that in the F; hybrids of 4. fatuaX A. sterilis 
the B-factor was completely dominant and the segrega- 
tion of later generations showed it to be due to a unit 
factor difference. Similarly Florell (1981) reported that 
in various crosses of A. sterilis with A. fatua the B-factor 
was dominant in the F), while the F2 segregated in the 
ratio of 3 sterilis-like : 1 fatwa-like for this character. 
Florell also crossed A. sterilis with A. sativa and found 
the F, plants to have non-articulate lower florets (spike- 
lets) as in A. sativa, as well as non-articulate upper florets 
as in both parents. However, when the upper florets 
were separated by fracture, the rachilla segment remained 
with the floret above as in A. sterilis. The F's segre- 
gated in the ratio of 1 sativa-like : 2 intermediate, like 
the F, : 1 sterilis-like, indicating linkage for the B- and 
C-factors. No cross-over plants were found. 
Nishiyama (1935) obtained further evidence on the 
nature of the B-factor by crossing A. sterilis with a het- 
erozygous fatuoid from A. sativa having only one C- 
chromosome. Plants were obtained in the F2 which had 
40 chromosomes, thus lacking the C-chromosome en- 
tirely. Such plants were fatuoids having the grain char- 
[ 291 ] 
