Sudan Grass. 23 Tho seed of Sudan grass resembles Johnson grass seed very closely, except that it is larger and more plump, (Fig. 10.) No machinery for separating the two kinds of seed has been devised; hence the only way of obtaining pure Sudan grass seed is to guard against its mixture with Johnson grass during tho growing period and in the thrashing process. South of 38° north latitude, indicated on the map shown as figure 3, Johnson grass behaves as a perennial and is troublesome because it is difficult to eradicate. North of the thirty-eighth parallel of latitude, roughly speaking, Johnson grass is not troublesome, because it usually is killed by the winter freezes. A slight admixture of Johnson grass in tho Sudan grass seed sown for hay production north of the thirty-eighth parallel is no great disadvantage.

FIG. 10.—Seeds of Johnson grass (left) and Sudan grass (right) showing their comparative size and their similarity in shape.

South of this lino, where Johnson grass is likely to become a pest, care must be used to see that the Sudan grass seed is free from Johnson grass seed.

The following suggestions may be remembered with advantage by the farmer in the Southern States : A fanner may grow sufficient seed for his own plantings and thus be assured of its purity; when he finds it necessary to buy Sudan grass seed and his land is free from Johnson grass, he should purchase only that grown outside tho Johnson grass region or from responsible growers in the South who can guarantee the purity of tho seed. If tho Sudan grass is to be ' seeded on land already containing Johnson grass, the presence of seed of the latter is a matter of small importance.

The presence of even a small number of Johnson grass seeds can be detected by a properly trained seed analyst. A method for their identification has been formulated by F. H. Hillman, of the United States Department of Agriculture, and is described fully in Department Bulletin 406.

A point to be remembered in the production of Sudan grass seed is that tho plant hybridizes very freely with sorghum, especially with