Thus it appears that the cultivated diploid and tetra- 
ploid oats arose from their wild ancestors by recessive 
mutation. The geographic isolation of both species from 
the main populations of the wild diploid and tetraploid 
species has undoubtedly been an important factor in the 
evolution of these oats. 
Avena sativa 
The common cultivated oat is generally believed to 
have arisen from A. fatwa, In addition to its lack of 
floret-articulation, the cultivated species is distinguished 
from its putative ancestor by lacking prominent hairs 
about the base of the lemma and by having greatly re- 
duced dorsal awns. The inheritance of these characters 
in crosses between the two species has been investigated 
by many workers (see Huskins, 1946) and the combina- 
tion of characters behaves genetically as if due to a single 
gene or gene complex. The F; is intermediate between 
the two parents in having a twisted geniculate awn only 
on the lower floret, while the pubescence and articulation- 
surface are much reduced compared to A. fatwa. The 
F2 segregates in the ratio 1 sativa-like : 2 intermediate : 
1 fatua-like for these characters. 
Considerable light has been shed on the nature of the 
genetic factor governing the distinction between these 
two species by the study of fatuoids or false wild oats. 
This problem has been extensively reviewed by Huskins 
(1946), so only the barest outlines will be presented here. 
Fatuoids are derivatives or ‘‘off types’’ of 4. sattva which 
arise spontaneously in many varieties of the cultivated 
oats and resemble 4. fatwa in type of floret-articulation, 
grain-pubescence and awn-development, but resemble 
the variety from which they arose in all other characters. 
Huskins presents convincing evidence that fatuoids are 
caused by chromosome aberrations which give rise to 
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