A Classification of the Varieties of Cultivated Oats 103 
In the present classification the number of nerves in the glume and in 
the lemma, and the prominence of nerves in the latter structure, are used 
as descriptive terms and sometimes to aid in the identification of varieties. 
The number of nerves in the glume varies from seven to thirteen, but 
in most varieties it is usually nine; in the lemma the usual number is 
seven, although the limits are from five to ten. The prominence of the 
nerves is a relative character the estimation of which must be left to the 
judgment of the investigator. The number and the prominence of the 
nerves are inheritable characters and in a given variety do not vary beyond 
the characteristic limits. The nerves of the glumes may easily be counted 
in the green spikelet, while those of the lemma are more distinct in the 
matured grain. 
THE AWN 
The awn, or beard, of Avena is an extension of the midrib of the lemma, 
emerging from the epidermis at about the middle of the grain. In wild 
forms it thus appears on all grains of the spikelet, and usually is genic- 
ulate and, below the knee, twisted (Plate I, 1, a). The form and the per- 
sistence of the awn are usually included by botanists in descriptions of 
Avena species. In most cultivated varieties the awn is carried only by 
the lower grain, and is usually straight, weak, and scarcely twisted. 
A few cultivated varieties, however, have awns which are rather strongly 
twisted and occasionally geniculate. Trabut (1911), in tracing a series 
of A. sterilis between the wild and the cultivated types, observed a grad- 
ual reduction in the number of awns per spikelet and in their genicu- 
late and twisted form. Zade (1912), On crossing a cultivated variety with 
A. fatua, found that in hybrids of the first generation the lower grain 
only of the spikelet was bearded. Nilsson-Ehle (1914) found awns to be 
produced more numerously by white and black grains than by yellow 
grains, the latter apparently containing a factor which inhibited their 
development. 
The appearance of numerous strong awns in cultivated oats is regarded 
by many as a mark of degeneracy resulting from unfavorable conditions 
for growth. There is not sufficient evidence, however, to prove that such 
so-called reversions are anything more than intermediate forms which 
occur in the mixed population of cultivated oats; for, while certain vari- 
eties are awnless, many of the best varieties, as Swedish Select, have 
numerous, rather strong, awns, and frequently in varieties of the A. sterilis 
