began to deteriorate (from about 2000 B.C. on, according 
to Werth), the oats were better adapted to the changed 
conditions and supplanted the emmer. 
The existence of oats as weeds of other cereals un- 
doubtedly has had a profound influence upon the evolu- 
tion of the genus. In the first place any mutation in a 
wild weed-oat causing non-articulate florets would have 
a selective value, as those grains which did not fall would 
be harvested with the main crop and planted next year. 
Similar mutations arising in the wild would be lethal. 
Some species of the genus, with man as an agent of 
dispersal, have spread far from their native homes. No 
doubt A. strigosa and A. abyssinica achieved geographic 
isolation in this way, while 4. sativa and A. fatua have 
encircled the globe. These species have achieved vastly 
larger populations than they would have otherwise, and 
the survival of new mutants under differing ecological 
conditions must have added greatly to the total varia- 
bility of the species. In addition, the dispersal of oats 
by man probably has brought together species which 
were once isolated geographically, thus facilitating hy- 
bridization. At present we can but dimly see how this 
process has added to the variability of 4. sterilis and A. 
fatua, but perhaps it explains why A. sterilis ssp. Lu- 
doviciana resembles A. fatua, within whose range it lies, 
while A. fatua ssp. meridionalis which lies within the 
range of fl. sterilis has the largest spikelets of the fatua 
group. 
Modern Oats 
It is fitting to end this review with a tribute to the 
many oat breeders who, during the past half century, 
have dedicated themselves to the never-ending battle 
against parasitic fungi. It has been found that the pri- 
mary sources of disease resistance in oats are 4. byzantina 
and A. sterilis (Coffman, 1946), and oat-breeding projects 
[ 298 ] 
