amount of light on the origins of the polyploid species, 
as well as the relationships between species having the 
same chromosome number. 
Diploid < Diploid—Genome analyses between diploid 
Avena species have been restricted to the series Hubar- 
batae. The F, of A. strigosa brevis XA. strigosa showed 
normal bivalent formation (Ellison, 1988). The chromo- 
somes of 4. Wiestiu are very similar to those of A. stri- 
gosa, as Nishiyama (1988) crossed these two species with 
a synthetic diploid and 7 normal bivalents were observed 
in the F; of both crosses. 
The chromosomes of A. hirtula show slight structural 
differentiation from those of A. strigosa, for in the F; of 
A lirtulaX A. strigosa brevis Ellison (1940) found com- 
plete pairing in most cells, but 1% of the cells examined 
showed 6 bivalents and 2 univalents while in many cells 
1 bivalent was found to consist of heteromorphic homo- 
logues. Greater differentiation is shown by the oat 
€c1795 which has been crossed with A. Wiesti and A. 
strigosa brevis (Ellison, 1940), and in both eases 5 biva- 
lents and 1 quadrivalent were regularly observed. 
The above evidence suggests the chromosomes of A. 
strigosa, A. Wiestu and the synthetic diploid are very 
similar. Nishiyama (1986) has represented the genome 
of these species as AA. Although showing some differ- 
entiation, the genome constitution of A. hirtula and 
Ce1795 appears to be AA also. 
Tetraploid< Tetraploid— Ellison (1988) observed mei- 
otic behavior in the F; of A. barbataX A. abyssinica and 
found complete bivalent formation in most cells. How- 
ever, 159% of the cells showed 1 quadrivalent and cells 
having no quadrivalent sometimes had 2 or 4 univalents 
or aunivalent and atrivalent. Ellison believed this irreg- 
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