448 THE SMALL GRAINS 



Seeds of penny cress occur in millet, clover, cereals, and 

 flaxseed. They are readily separated from cereal kernels 

 with ordinary cleaning machines. The plants should 

 be prevented from maturing their seeds, which is difficult, 

 as they mature at different times. When many of the 

 plants are found in the growing grain, harrowing with 

 the toothed harrow, when the crop is 3 to 4 inches high, 

 will do good. Disking at once after harvest and plow- 

 ing later will kill most of the weeds. Seeding down to 

 grasses and clovers will effect complete eradication. 



487. Wild oats (Avena fatua, Linn.). Several species 

 of oats are wild in this country, of which this. one is a per- 

 nicious weed, particularly in the northwestern and Pacific 

 Coast states and western Canada. Unlike chess, wild oats 

 occurs more commonly in spring grain than in winter grain. 



Wild oats grows from 2 to 4 feet high, in tufts. The plant closely 

 resembles some cultivated oat varieties. The panicle, at first com- 

 pact, soon spreads out 6 to 12 inches in all directions. The kernels 

 vary greatly in size, but are brown or gray or nearly black, sometimes 

 yellowish white. They are similar to those of many cultivated 

 varieties, but differ in being slimmer and harder, in having a horny 

 appearance, and besides exhibit the following differentiating char- 

 acters : The strongly bent and twisted awn, often broken off in 

 thrashing; the slanting, horseshoe-shaped scar at the base of the 

 lemma, sometimes broken off in handling ; the stiff bristles surround- 

 ing the basal scar, which are not, however, always present in thrashed 

 grain ; the rachilla bearing the second kernel, but which remains 

 attached to the lower kernel after thrashing, is larger, and the free 

 end is slanting, roughly triangular, and shows a marked depression ; 

 the abundance and roughness of the hairs covering the kernel (Fig. 

 142 6). 



Three fixed forms of wild oats appear to have been 

 identified as follows : (1) Wild oats proper, taller than 

 cultivated oats, having dark brown or almost black ker- 



