Sudan Grass. 19 The following suggestions may be remembered with advantage by the farmer in the Southern States: A farmer 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 the Johnson grass region or from responsible growers in the South who can guarantee the purity of the seed. If the 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 the plant hybridizes very freely with sorghum, especially FIG. 10.- -Set'ds of Johnson grass (left) and Suoan prass (right) parative size and their similarity in shape.

showing their comwith the sorgos. In dry'regions where the pollen is carried for considerable distances by the wind, a Sudan grass field intended for a seed crop should be 60 to 80 rods from any sorghum. Another source of cross-pollination exists in the volunteer plants of sorghum sometimes found in fields that were planted to sorghum the previous year. To avoid such sources of trouble, fields that have been growing other crops than sorghum should be chosen for the Sudan grass seed crop.

To make sure of pure seed, roguing the field at least once a year must be resorted to, and the rogues should be removed before a chance has been afforded for cross-pollination. The great need of special efforts to keep Sudan grass pure is illustrated by the present condition of the sorgos, very few fields of which are to be found anywhere that are pure as to variety. They are very commonly mixed not only with other varieties of sorgo, but also with the grain sorghums. Unless seedsmen and growers unite in an effort to keep their seed fields free from sorghum hybrids, Sudan grass will lose much of its distinctiveness withn the next 20 years.