of two sections: Huwavena Griseb., which contains the 
cultivated oats and related wild annuals; and Avenastrum 
C. Koch, which comprises about forty species of wild per- 
ennials, most frequent in northern Eurasia, but with two 
species native to western North America. By recent 
authors (Hitchcock, 1950; Clapham et al., 1952) the sec- 
tion Avenastrum is treated as the genus Helictotrichon 
Besser. In the present paper only the section Muavena 
will be considered. 
Natural Systems of Classification 
Three students, Cosson (1854), Thellung (1911) and 
Mal’tsev (1929), have each attempted to devise a natural 
classification for the section Huavena. 
Cosson divided the section into subsection Sativae con- 
taining the cultivated species, and subsection 4 grestes 
containing the wild. This division is based on the fact 
that the spikelets of the cultivated species are firmly at- 
tached to the rachilla and do not fall at maturity, whereas 
the spikelets of the wild species are articulated to the 
rachilla and fall spontaneously when ripe. Cosson further 
divided the Agrestes into the series Biformes in which 
only the lower floret is articulated so that the spikelet 
falls as a unit, and the series Conformes with all florets 
articulated and falling separately. The disposition of 
species by Cosson is: 
Subsect. I. Sativae 
A, sativa, A. orientalis, A. strigosa, A. brevis, A. nuda 
Subsect. Il. Agrestes 
Series 1. Biformes 
A. ventricosa, A. sterilis, A. eriantha 
Series 2. Conformes 
A. longiglumis, A. clauda, A. hirsuta, A. fatua 
The system of 'Thellung is based on the assumption 
that each of the cultivated species is related to and de- 
rived from some wild species. Accordingly the Sativae 
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