A Classification of the Varieties of Cultivated Oats 89 
Double grains. — When under unfavorable weather conditions at maturity the outer 
grain fails to become fully developed, its lemma often completely envelops the inner grain 
and causes the condition of "double grain." Because of this abnormality, double grains 
are of no importance in classification, but they should never be confused with single grains. 
According to Atterberg none of the above four forms of spikelets are 
carried by every variety in like number, and it is only the prevailing form 
in a given variety that determines its group relationship. Classes arranged 
on this basis, therefore, cannot be constant, but are transitional, passing 
into one another under changes in climatic and soil conditions; and hence 
no variety can by this system rightly be classified under a single con- 
dition of environment. 
The following forms of grains are believed by Atterberg to be more 
constant than the number of grains in the spikelet: 6 
"Barley" grains. — Single grains prevail in this type, but the second grain, when present, 
shows the same short, heavy, full, compact form as the first grain. The lemma is strongly 
developed and on single grains nearly, often entirely, covers the palea. If the palea is not 
visible the grain is called "closed"; if a part of it can be seen the grain is designated as 
"open." When the second grain is present the lemma of the outer grain commonly has its 
edges so inrolled as to form a gutter. 
Pointed grains. — The grain of this type is widest at, or just below, the upper end of the 
rhachilla; it is longer than the "barley" type and the edges of its lemma are rolled into a 
hard, stiff point. Spikelets with 2 grains are more numerous than in "barley" oats, 1-grained 
spikelets seldom predominating. In all other respects of shape than those mentioned the 
grains are similar to the "barley" type. 
Full, 'plump grains. — Grains of this type are rich in kernels; they are full, plump, short, 
and borne on weak peduncles; and the inner side of the first grain is strongly convex 
as compared with the usual guttered form. The lemma is more free from the caryopsis 
than in most forms. If the point of the grain becomes weak and longer drawn, the form 
passes to the pointed-grain type. 
Short grains. — When grains of the above type become weaker and more convex on their 
inner side they assume a shorter, rounder form and pass to the short-grain type. The edges 
of the lemma then cover the greater part of the palea. 
Hulled grains. — In northern Germany a very long, thin, long-pointed type is called 
"chaffy" or "hully" (spelzig) oats. This type has many 3-grained spikelets. 
Aside from its comprehensive descriptions of spikelet and grain forms, 
Atterberg's classification is subject to criticism because of the characters 
used to distinguish main groups of varieties. The absolute weight of 
grains, their kernel content, and their form, are too easily influenced by 
environment to afford a reliable means of distinction; there would be, in 
response to change of climate and soil, an interchange of varieties among 
groups thus characterized. Again, by Atterberg's method of grouping, 
varieties morphologically unlike may be brought together; and, on the 
6 Translation from the original German. 
