A Classification of the Varieties of Cultivated Oats 109 
German oats, proportions of double-grains ranging only from 0.3 to 4.4 
per cent of the total number of grains. The value of double-grains as a 
character in classification is therefore only local, and their occurrence in 
certain varieties may in moct cases be considered a measure of the lack 
of adaptability of the variety to its environment. However, since the 
limits of environment under which double-grains predominate in certain 
varieties cannot be stated, they must in such cases be accepted as a varietal 
characteristic, subject, perhaps, to place variation. On that basis they 
are used in the present classification as a supplementary character for 
the identification of the few varieties in which, under this environment, 
they form the typical predominating spikelet. 
Double-grains may readily be identified when mature. Many observers, 
however, have apparently mistaken double-grains for the very unusual 
single-grained spikelet. One rarely finds a so-called single-grained spike- 
let which on examination does not prove to be really a double-grain 
with the first or the second grain, or both, defective or rudimentary. 
the spikelet 
Without considering separately its parts, the spikelet as a morphologic 
entity presents only two characters useful in classification, namely, its 
attitude and the number of grains it carries. 
Attitude of spikelets 
In different varieties the attitude of the spikelets may be observed as 
pendant, pectinate, and confused (pointing in all directions) (figs. 12, 
13, and 14, respectively). All these forms are found among varieties of 
A. sativa orientalis and they are in some cases useful in classifying the 
members of that group. In all other varieties, however, only the pendant 
form is found, and hence no distinction by the attitude of spikelets is to 
be made outside of the A. sativa orientalis group. 
Number of grains in spikelet 
In the common cultivated forms of oats the number of grains carried 
by the spikelet ranges from one to three, with the exception of A. nuda, 
the spikelets of which often bear four, five, or even six grains. There 
are no varieties bearing exclusively one-, two-, or three-grained spikelets, 
